DWQ-2008-020004

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PIUTE RESERVOIR

LIMNOLOGICAL ASSESSMENT OF WATER QUALITY

Photo Provide By: Sevier River Water Users Association

Utah Division of Water Quality

February 2008

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Table of Contents
TABLE OF CONTENTS............................................................................................................. 2
EXECUTIVE SUMMARY .......................................................................................................... 4
1.0 INTRODUCTION .................................................................................................................. 5
1.1. Piute Reservoir Impairment...................................................................................5
1.2. EPA Delisting Requirements ..................................................................................5
2.0 WATER QUALITY ASSESSMENT.................................................................................... 6
2.1. Beneficial Use Classification...................................................................................6
2.2. Water Quality Standards........................................................................................6
2.3. Water Quality Data Analysis..................................................................................8
2.3.1. Analytical Methods................................................................................................... 8
APHA Methods............................................................................................................. 8
USEPA Methods........................................................................................................... 8
Utah DWQ Generic Methods (generic method and generic method 2)........................ 8
Utah DWQ Field Measures........................................................................................... 8
2.3.2. Quality Assurance/Quality Control........................................................................... 9
Treatment of Nondetects............................................................................................... 9
Treatment of Errors....................................................................................................... 9
Treatment of Outliers.................................................................................................... 9
2.4. Beneficial Use Support Assessment........................................................................9
2.4.1. Dissolved Oxygen..................................................................................................... 9
2.4.2. Dissolved Oxygen Saturation ................................................................................. 11
2.4.3. pH............................................................................................................................ 11
2.4.4. Temperature............................................................................................................ 12
2.4.5. Total Phosphorus .................................................................................................... 12
2.4.6. Chlorophyll a.......................................................................................................... 14
2.4.7. Secchi Depth........................................................................................................... 15
2.4.8. Water Column Data Assessment ............................................................................ 16
2.4.9. Diurnal DO Data..................................................................................................... 21
2.4.10. Trophic State Index............................................................................................... 23
2.4.11. Fishery Management............................................................................................. 27
2.4.12. Phytoplankton composition .................................................................................. 28
2.4.13. Existing Watershed TMDLs................................................................................. 28
3.0 WATER QUALITY SUMMARY ....................................................................................... 32
3.1. Compliance with Water Quality Criteria............................................................32
3.2. Explanation of Exceedances..................................................................................32
3.2.1. Total Phosphorus .................................................................................................... 32
3.2.2. Temperature............................................................................................................ 32
3.2.3. Diurnal Profile Sampling........................................................................................ 32
3.3. Trophic State..........................................................................................................32
3.4. Watershed TMDLs ................................................................................................33
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REFERENCES............................................................................................................................ 34

LIST OF TABLES
Table 2.1. 3A Water Quality Numeric Standards and Pollution Indicator Values (Utah
State Code RS 317-2-14)...........................................................................................7
Table 2.2. Percent of Water Column Profile Exceeding 4 mg/L Dissolved Oxygen. ..............11
Table 2.3. Piute Reservoir Percent Dissolved Oxygen Saturation............................................11
Table 2.4. Piute Reservoir depth integrated pH values.............................................................12
Table 2.5. Summary of Total Phosphorus Data in Piute Reservoir watershed.........................14
Table 2.6. Piute Reservoir Chlorophyll a Data (µg/L) Summary.............................................14
Table 2.7. Piute Reservoir Secchi Depth Summary..................................................................16
Table 2.8. Depth Integrated Profile Sampling Frequency. .......................................................17
Table 2.9. Trophic State Index Categories................................................................................23
Table 2.10. Mean TSI Values in Piute Reservoir. ..............................................................24
Table 2.11. Average Total Phosphorus Load and TMDL Targets......................................31

LIST OF FIGURES
Figure 2.1. Total phosphorus trend data for Piute Reservoir.....................................................13
Figure 2.2. Chlorophyll-a data for Piute Reservoir....................................................................15
Figure 2.3. Secchi depth measurement for Piute Reservoir since 1999.....................................16
Figure 2.4. Depth Integrated Profile Summary for Piute Reservoir Above the Dam. ...............17
Figure 2.5. Depth Integrated Profile Summary for Piute Reservoir at Mid-Lake......................18
Figure 2.6. Depth Integrated Profile Summary for Piute Reservoir in the Upper
Reaches....................................................................................................................18
Figure 2.7. Typical Depth Integrated Profile Sample at the Dam Site During Critical
Conditions (7/28/2005)............................................................................................19
Figure 2.8. Typical Depth Integrated Profile Sample at the Mid-Reservoir Site During
Critical Conditions (7/28/2005)...............................................................................20
Figure 2.9. Typical Depth Integrated Profile Sample at the Upper Reservoir Site During
Critical Conditions (7/28/2005)...............................................................................20
Figure 2.10. Diurnal Profile Data for the Piute Reservoir Dam Site....................................22
Figure 2.11. Trophic State Index Trend Data for the Piute Reservoir Dam Site.................24
Figure 2.12. Trophic State Index Trend Data for the Piute Reservoir Mid-Reservoir Site........25
Figure 2.13. Trophic State Index Trend Data for the Piute Reservoir Upper Reservoir
Site.........................................................................................................................25
Figure 2.14. TSI Relationships for the Piute Reservoir Dam Site. ......................................26
Figure 2.15. TSI Relationships for the Piute Reservoir Mid-Reservoir Site........................27
Figure 2.16. TSI Relationships for the Piute Reservoir Upper Lake Site............................27
Figure 2.17. Average Total Monthly Inflow to Piute Reservoir..........................................29
Figure 2.18. Average Monthly Inflow Total Phosphorus Concentrations...........................29
Figure 2.19. Average Total Monthly Total Phosphorus Load and Loading Capacity.........30

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EXECUTIVE SUMMARY
The designated beneficial uses for Piute Reservoir are secondary contact recreation (2B),
cold water game fish and the associated food chain (3A), and agricultural water supply
(4). The cold water game fish designated use (3A) was identified as partially supporting
on the 2006 303(d) list because of elevated in-lake total phosphorus concentrations.
However, analysis of current water quality data indicates that the reservoir is currently
supporting its 3A designated beneficial use. Piute Reservoir is recommended to be
placed in Category 5B of the State of Utah’s 303(d) List and requested for removal from
the current listing of impaired waters based on the following elements:
• Current and historical dissolved oxygen data indicate greater than 50% of the
water column has more than 4 mg/L dissolved oxygen in all depth integrated
profile samples.
• Total phosphorus concentrations are greater than the in-lake State indicator value
of 0.025 mg/L; however, reservoir productivity is less than expected with current
phosphorus levels.
• TSI values indicate that the reservoir is mesotrophic the majority of the time with
eutrophic conditions in late summer that correspond to the period after de-
stratification.
• Exceedances of the in-lake pH standard do not occur.
• Exceedances of temperature criteria were determined to be naturally occurring.
• No fish kills have been reported.
• Some blue-green algal species are present in the late summer and early fall, but
the limited dataset show low relative abundance.
• Additionally, TMDLs developed for total phosphorus for the East Fork Sevier
River and the Sevier River, which provide 100 percent of the inflow to Piute
Reservoir, will reduce total phosphorus loads to the reservoir by approximately 50
percent.

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1.0 INTRODUCTION
1.1. Piute Reservoir Impairment
Piute Reservoir was identified as water-quality limited due to excess in-lake phosphorus
concentrations. Piute Reservoir’s beneficial uses are secondary contact recreation (2B),
cold water game fish and the associated food chain (3A), and agricultural water supply
(4). The cold water game fish designated use (3A) was identified as partially impaired on
the State of Utah 2006 303(d) list. The secondary contact recreation and agricultural
water supply designated uses were assessed as fully supported on this same list.
1.2. EPA Delisting Requirements
Analysis of current water quality in Piute Reservoir indicates that the reservoir is meeting
all designated beneficial uses. Piute Reservoir is recommended to be placed in Category
5B of the State of Utah’s 303d List and requested for removal from the current 303(d)
listing of impaired waters.
According to EPA regulations, each State must demonstrate good cause for not including
waters on the list (40 C.F.R. Part 130.7(b)(6)(iv)) or removing them from the list. These
include:
• A water body listed due to error in assessment or because a water body was listed
incorrectly in place of another water body or any other error not based on a water
quality assessment.
• The most recent data assessment indicates that the water body is supporting all of
its designated beneficial uses.
• A total maximum daily load analysis has been completed and approved by EPA.
• New modeling information indicates no TMDL is required in order to maintain
water quality standards.
• Data assessment methodologies have been modified.
Utah may also recommend delisting of a water body when:
• The water body is meeting all applicable water quality standards or is expected to
meet these standards in a reasonable time frame (e.g., two years) as a result of
implementation of required pollutant controls or
• If, upon re-examination, the original basis for listing is determined to be
inaccurate.
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2.0 WATER QUALITY ASSESSMENT
2.1. Beneficial Use Classification
The State of Utah has designated the beneficial uses of Piute Reservoir to be: secondary
contact recreation (2B), cold water game fish and the associated food chain (3A), and
agricultural water supply (4). The cold water game fish designated use (3A) was
identified as partially supporting on the State of Utah 2006 303(d) list. Secondary contact
recreation and agricultural water supply designated uses were reported as being fully
supported on this same list.
Waters designated for cold water game fish and associated food chain use are required to
exhibit appropriate levels of dissolved oxygen, temperature, pH, ammonia and turbidity
for cold water aquatic life support. Piute Reservoir is not listed as impaired for
temperature or pH. The analysis presented in section 2.4.4 of this assessment indicates
that exceedances of the water temperature criteria are associated with natural conditions.
2.2. Water Quality Standards
Water quality standards under the Clean Water Act consist of three main components:
designated beneficial uses, water quality criteria that are established to protect designated
beneficial uses, and anti-degradation policies and procedures.
Water quality criteria can be either numeric limits for individual pollutants and
conditions, or narrative descriptions of desired conditions. Table 2.1 summarizes the
applicable State of Utah water quality criteria for the 3A beneficial use impairment to
Piute Reservoir.

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Table 2.1. 3A Water Quality Numeric Standards and Pollution Indicator Values (Utah State Code RS 317-2-14)
Parameter
and
Designated
Beneficial
Use
Criterion Utah State
Code
Comments
Dissolved Oxygen (DO)
2B N/A
3A No less than 6.5 mg/L (30-day average), 9.5 early life stages /
5.0 all life stages (7-day average), 8.0 early life stages / 4.0 all
life stages (1-day average)
Table 2.14.2 These limits are not applicable to lower water levels in deep
impoundments.
4 N/A
Total Phosphate as P (pollutant indicator value)
2B No greater than 0.05 mg/L Table 2.14.1
3A No greater than 0.05 mg/L Table 2.14.2
4 N/A
Total phosphorus as P (mg/L) limit for lakes and reservoirs shall
be 0.025 mg/L.
pH
2B No less than 6.5 AND no greater than 9.0 pH units Table 2.14.1
3A No less than 6.5 AND no greater than 9.0 pH units Table 2.14.2
4 No less than 6.5 AND no greater than 9.0 pH units Table 2.14.1
Total Dissolved Gas
2B N/A
3A Not to exceed 110% of saturation. Table 2.14.2
4 N/A
Temperature
2B N/A
3A No greater than 20 oC, No greater than 2 oC change Table 2.14.2
4 N/A
The temperature standard shall be at background where it can be
shown that natural or un-alterable conditions prevent its
attainment. In such cases rulemaking will be undertaken to modify
the standard accordingly.

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2.3. Water Quality Data Analysis
2.3.1. Analytical Methods
Data collected and assessed for Piute Reservoir water quality analysis consisted of samples
evaluated by four primary categories of analytical methodology: APHA, USEPA, Utah DWQ
generic and Utah DWQ field methods.
APHA Methods.
Refers to American Public Health Association (APHA), Standard Methods for the Examination
of Water and Wastewater, 18th edition (1992), American Public Health Association, 1015
Fifteenth Street, NW, Washington, DC 20005 (from
http://www.epa.gov/STORET/metadata.html).
APHA approved methods specific to the available data for Piute Reservoir include analytical
procedures for measuring alkalinity, chemical oxygen demand, chloride, chlorophyll, dissolved
solids, fecal coliform bacteria, fecal streptococcus group bacteria, fixed solids, pH, total coliform
bacteria, total organic carbon, total suspended solids, volatile solids, and others not pertinent to
this TMDL effort.
USEPA Methods
Refers to US Environmental Protection Agency (US EPA), Methods for Chemical Analysis of
Water and Wastes (1983), USEPA, EPA 600/4-79-020 (from
http://www.epa.gov/STORET/metadata.html).
USEPA approved methods specific to the available data base for Piute Reservoir TMDL include
analytical procedures for measuring ammonia, biochemical oxygen demand, chloride, nitrate +
nitrite, phosphorus, specific conductance, total suspended solids, turbidity, volatile solids, and
others not pertinent to this TMDL effort.
Utah DWQ Generic Methods (generic method and generic method 2)
Refers to Utah Division of Water Quality (DWQ) entered in the STORET data base where
historical methodology may not be available, method is listed as unknown, method is listed as no
cite, method is listed as Method not cited, or others.
UTAH DWQ GENERIC METHODS (GENERIC METHOD AND GENERIC METHOD 2)
specific to the available data base for Piute Reservoir TMDL include measurements of alkalinity,
ammonia, biochemical oxygen demand, chemical oxygen demand, chloride, chlorophyll a,
nitrate, nitrate + nitrite, nitrite, pH, ortho-phosphate, phosphorus, specific conductance, total
Kjeldahl nitrogen, total organic carbon turbidity, and others not pertinent to this TMDL effort.
Due to the fact that the data in this analysis category were collected, reviewed and submitted to
the STORET database by DWQ, it was assumed that all sampling protocols and analytical
methods employed were carried out in a fashion approved by DWQ and contained and attained a
DWQ-approved level of quality assurance and quality control.
Utah DWQ Field Measures
Refers to Utah Division of Water Quality (DWQ), Quality Assurance/Quality Control Manual
(1996). Utah DWQ Field Measures approved methods specific to the available data base for

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Piute Reservoir TMDL include analytical procedures for measuring chlorine, dissolved oxygen,
flow, pH, salinity, Secchi depth, specific conductance, and temperature (air and water).
2.3.2. Quality Assurance/Quality Control
The data were assessed to ensure that all data points included in the process met an appropriate
level of quality. Basic statistical analyses were used to characterize data the range and quality.
Statistical parameters assessed included the number of data points, determination of mean,
median, maximum and minimum values, assessment of variance and an analysis of seasonality.
The completeness of the data set was also evaluated in a spatial, temporal and parameter-specific
fashion and critical data gaps were identified. Further evaluation is discussed in the following
sections.
Treatment of Nondetects
Some the data points collected in this dataset are concentration values identified as below
detection limits. Standard methods were used to statistically interpret these values. This was
accomplished by assigning a numeric value of one-half of the detection limit (in the case of
concentrations identified as below detection limits.
Detection limits are reported in the STORET database for most data points and provided a
specific nondetect values for most data. If data point specific detection limits were not provided,
detection limits were applied based on specific analytical methods.
Treatment of Errors
An initial assessment of the data was performed to identify transcription and other errors such as
inappropriate values inaccurate sample information, and errors in physical information. No such
errors were identified in this analysis.
Treatment of Outliers
To identify data representative of water quality conditions in the Piute Reservoir, a threshold of
plus or minus three standard deviations from the mean was applied to the available data sets for
relevant in-lake water quality data. The exclusion of these outlier had an insignificant effect on
mean concentrations for total phosphorus, chorlophyll-a, temperature, pH, secchi depth,
dissolved oxygen, and dissolved oxygen saturation.
2.4. Beneficial Use Support Assessment
2.4.1. Dissolved Oxygen
Dissolved oxygen (DO) is important to the health and viability of fish and other aquatic life.
Aquatic life depends on high concentrations of dissolved oxygen from 6–8 mg/L or greater.
Dissolved oxygen concentrations below 5 mg/L can result in stress, reduced resistance to other
environmental stressors, and even death at very low levels (less than 2 mg/L).
In addition to direct effects on aquatic life, low dissolved oxygen concentrations can lead to
changes in water and sediment chemistry that can influence the concentration and mobility of
nutrients and toxins such as phosphorus, ammonia, and mercury. Low dissolved oxygen at the
sediment-water interface can result in substantial release of sorbed phosphorus in the overlying
water column, which in turn can lead to increased algal growth and decreased dissolved oxygen
concentrations. Finally, increased water column concentrations of ammonia can result from the

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chemical changes caused by anoxic conditions. Elevated ammonia levels threaten the health of
aquatic life forms and, at extreme concentrations, can result in death.
Low dissolved oxygen often results from high nutrient, organic, or algal loading to a surface
water system. Nutrients promote algae growth, which in turn consumes oxygen from the water
column during night time respiration. In addition, dead algae and other organic matter settle to
the bottom of the water body where decomposition consumes oxygen.
Dissolved oxygen concentrations are also reduced by pollutants that require oxygen in oxidation
processes. Biochemical oxygen demand (BOD) is a measure of the dissolved oxygen required to
oxidize material. Some of the delivered organic material is algae and some is detritus, both of
which exert a certain amount of BOD. Additionally, organic loads delivered to the reservoir
during high volume and high velocity spring flow events can contribute to BOD.
Data collected in Piute Reservoir since 1999 indicate that dissolved oxygen concentrations are
generally high with mean concentrations ranging from 4.1 mg/L to 8.6 mg/L. Minimum
dissolved oxygen concentrations range from 0.15 to 7.5 mg/L and are limited to the sediment-
water interface at the bottom of the reservoir.
The State of Utah has defined the support status of game fish populations relative to the
percentage of the total water column experiencing depressed dissolved oxygen concentrations.
A water body's dissolved oxygen concentration is defined to be non-supporting for cold water
game fish when less than 25 percent of the water column depth exhibits dissolved oxygen
concentrations of 4.0 mg/L or greater. If 25 to 50 percent of the water column depth exhibits
dissolved oxygen concentrations of 4.0 mg/L or greater, the water body is defined to be partially
supporting. Where greater than 50 percent of the water column depth exhibits dissolved oxygen
concentrations of 4.0 mg/L or greater, a full-support status has been defined. These criteria were
assessed for each depth integrated profile sample.
Table 2.2 shows the percent of each water column profile with DO concentrations below 4.0
mg/L. Examination of the table shows that the reservoir is fully supporting the 3A DO criterion
and that no profile has greater than 31.1% of the profile with less than 4.0 mg/L.
Additionally, an examination of historical profiles collected between 1991 and 1997 show that
17 of 22 (77 percent) profiles had dissolved oxygen concentrations greater than 4.0 mg/L
throughout the entire water column. One profile observed on 8/8/1995 at the above dam site had
31 percent (the maximum observed) of the water column below 4 mg/L DO. Historic data
demonstrates no violations of the 50 percent water column 3A criteria.

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Table 2.2. Percent of Water Column Profile Exceeding 4 mg/L Dissolved Oxygen.
Site Name Month 2001 2003 2005 2007
May
June 0%
July 2.4% 28.1% 5.7% & 7.0%
Aug 0% 33.1%
PIUTE RES AB DAM 01
Sept 0%
May
June 0%
July 7.0% 31.6% 16.4
Aug 0% 20.2%
PIUTE RES MIDWAY UP LAKE 02
Sep 0%
May
June 0%
July 0% 0% 0%
Aug 0% 0%
PIUTE RES UPPER REACHES 03
Sep 0%

2.4.2. Dissolved Oxygen Saturation
The water quality criteria for dissolved gases established by the State of Utah is a maximum
saturation of 110% due to the stress supersaturated water can cause for fish. Dissolved oxygen
supersaturation (concentrations greater that 110% of saturation) was experienced in 6.8% of
recent samples collected in the water column profiles throughout the reservoir. 5.7 percent of
water column samples were greater than 110 percent saturations at the dam site, while 7.5
percent and 7.8 percent of samples were greater than the standard at the mid lake and upper
reaches site, respectively (Table 2.3). Additionally, available historic profiles do not
demonstrate exceedances of the 100% DO saturation criteria.

Table 2.3. Piute Reservoir Percent Dissolved Oxygen Saturation.
Site Name Start End n
Min
(%)
Average
(%)
Max
(%)
n >
110
%
PIUTE RES AB DAM 01 7/5/2001 9/6/2005 88 1.8 76.7 126.7 5
PIUTE RES MIDWAY UP LAKE 02 7/5/2001 9/6/2005 69 2.2 77.3 128.7 5
PIUTE RES UPPER REACHES 03 7/5/2001 9/6/2005 38 60.6 90.0 121.3 3

2.4.3. pH
A key indicator of acidity or alkalinity of a system is pH, as measured by the hydrogen ion
activity in the water. A pH value of 7.0 is neutral, with values from 0–7 indicating acidic water
and values those from 7–14 indicating alkaline water. Extremely acid or alkaline waters can be
toxic to aquatic life. Even at less extreme levels, acidic or alkaline conditions can cause
chemical shifts in a system; acidic conditions can release metallic compounds from sediments
while alkaline conditions can increase ammonia toxicity and release sorbed phosphorus.

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Piute Reservoir pH observations are displayed in Table 2.4. The table shows that the minimum
and maximum observed pH values observed for each in-lake site during depth integrated
sampling are 7.4 and 8.8, respectively. A review of all available pH data throughout the entire
data record reveals no exeedances of the State’s minimum and maximum pH standard for the 3A
beneficial use. Additionally, an analysis of profile data presented in section 2.4.8 demonstrates
that pH values are very stable throughout the depth profile, which indicates that reservoir
productivity is not high enough to adversely affect water column pH.

Table 2.4. Piute Reservoir depth integrated pH values.
Site Name Start End Count Min Average Max
4949160 7/5/2001 9/6/2005 88 7.4 8.3 8.8
4949170 7/5/2001 9/6/2005 69 7.5 8.3 8.8
4949180 7/5/2001 9/6/2005 38 8.0 8.4 8.8

2.4.4. Temperature
High water temperatures can be harmful to fish at all life stages, especially when high
temperatures combine with other habitat limitations such as low dissolved oxygen or poor food
supply. As a stressor to adult fish, elevated temperatures can lower body weight, reduce oxygen
exchange, and diminish reproductive capacity. Extremely high temperatures can result in death
if they persist for an extended length of time. Juvenile fish are more sensitive to temperature
variations and duration than adult fish.
High water temperatures are routinely observed throughout the water column profile samples and
historic water samples in Piute Reservoir. Piute Reservoir was listed on the 2004 Utah 303(d)
list of impaired waters as partially supporting its 3A beneficial use for temperature. As the
reservoir has little natural cover and the watershed is located in an area experiencing warm, dry
climate conditions, the State of Utah conducted a heat budget analysis for the reservoir and
determined that the primary source of temperature loading was from solar radiation and heat
transfer. The heat budget analysis determined elevated water temperature was the result of
natural solar radiation.

2.4.5. Total Phosphorus
Excessive nutrient concentrations (nitrogen and phosphorus) can directly affect water quality by
causing algal blooms and excessive macrophyte growth, which can create objectionable odors
and appearance in water used for recreation. Excessive nutrient concentrations also have indirect
effects on water quality. During the daytime photosynthesis from algae produces excess oxygen;
however, at night time algae respire and consume sufficient oxygen from the water column that
can stress or kill fish and other aquatic organisms. Additionally, when algae die, they sink to the
bottom sediments where biochemical processes consume oxygen from the surrounding water.
Because most of the decomposition occurs in the lower levels of the water column, dissolved
oxygen concentrations near the bottom of lakes and reservoirs can be substantially depleted.

Where depth-integrated total phosphorus data are available for 1996 and 1998, concentrations
are observed to increase with depth during summer months. Concentrations in deeper water

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generally average about three times greater than concentrations at the water’s surface Mid-
Reservoir, and about six times greater than concentrations at the water’s surface at the dam.
Increases in total phosphorus with depth are generally correlated with low dissolved oxygen (less
than 3 mg/L) in the lower layers of the reservoir and most likely indicate dissolution from
sediment-bound phosphorus delivered during spring runoff.
Mean total phosphorus concentrations are presented in Figure 2.1 and summarized in Table 2.5
for all sampled depths at each site. Depth codes 21, 23, 27, and 29 correspond to the surface, 1
meter above the thermocline, 1 meter below the thermocline, and 1 meter above the bottom,
respectively. Mean concentrations range from 0.04 mg/L at the Dam Site to 0.09 at the mid-lake
site. Concentrations are generally lower in the surface water samples (depth of 21) than at the
bottom samples (depth of 29). This is most likely explained by the re-suspension of phosphorus
that occurs in anoxic conditions in the bottom of the reservoir.
The total phosphorus indicator concentration is 0.025 mg/L for lakes and reservoirs. The
indicator value is not considered a water quality standard but a pollution indicator level that is
used along with other water quality parameters to assist in the determination of the reservoir
impairment. While the majority of total phosphorus samples are greater than the indicator value,
expected levels of in-lake productivity and subsequent beneficial use impairment are not evident.
An analysis of the tropic state of the reservoir presented in section 2.4.10 demonstrates that algal
productivity is under-predicted by total phosphorus concentrations. One likely explanation is
that total phosphorus is bound to suspended particles and is unavailable for algal growth. A
more in-depth analysis of the reservoir’s trophic state is presented in section 2.4.10.

0
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(
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)
PIUTE RES AB DAM 01 PIUTE RES MIDWAY UP LAKE 02
PIUTE RES UPPER REACHES 03 TP Indicator Value Figure 2.1. Total phosphorus trend data for Piute Reservoir

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Table 2.5. Summary of Total Phosphorus Data in Piute Reservoir watershed.
Site Name Start End
Depth
Code Count
Min
(mg/L)
Average
(mg/L)
Max
(mg/L)
PIUTE RES AB DAM 01 6/17/1999 9/6/2005 21 7 0.01 0.04 0.06
PIUTE RES AB DAM 01 6/17/1999 9/6/2005 23 7 0.01 0.04 0.06
PIUTE RES AB DAM 01 6/17/1999 9/6/2005 27 7 0.02 0.04 0.07
PIUTE RES AB DAM 01 6/17/1999 9/6/2005 29 7 0.04 0.10 0.17
PIUTE RES MIDWAY UP
LAKE 02 6/17/1999 9/6/2005 21 7 0.01 0.04 0.07
PIUTE RES MIDWAY UP
LAKE 02 6/17/1999 9/6/2005 29 6 0.03 0.09 0.17
PIUTE RES UPPER
REACHES 03 6/17/1999 9/6/2005 21 7 0.01 0.05 0.15
PIUTE RES UPPER
REACHES 03 6/17/1999 9/6/2005 29 6 0.04 0.08 0.12

2.4.6. Chlorophyll a
Chlorophyll a is a pigment found in plants for use in photosynthesis. Chlorophyll a contained in
a reservoir can be used as a surrogate measure of phytoplankton production and as an indicator
of trophic state of the water body. A literature review regarding nuisance thresholds of algae
growth and chlorophyll a demonstrates that chlorophyll a concentrations between 10–15 μg/L
protect waters inhabited by salmonids (Pilgrim et al. 2001).
Current mean in-reservoir chlorophyll a concentrations range from 6.3 μg/L (Mid-Reservoir) to
8.4 μg/L (Upper Reaches) (Table 2.6). Figure 2.2 displays all chlorophyll a measurements in
Piute Reservoir since 1999. The figure demonstrates that chlorophyll a concentrations are
generally less than 10 μg/L.

Table 2.6. Piute Reservoir Chlorophyll a Data (µg/L) Summary.
Site Name Start End Count
Min
(ug/L)
Average
(ug/L)
Max
(ug/L)
PIUTE RES AB DAM 01 6/17/1999 9/6/2005 7 0.2 6.8 16.1
PIUTE RES MIDWAY UP LAKE
02 6/17/1999 9/6/2005 7 0.5 6.3 9.9
PIUTE RES UPPER REACHES
03 6/17/1999 9/6/2005 6 0.9 8.4 22.9

15
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6/
1
/
1
9
8
9
6/
1
/
1
9
9
0
6/
1
/
1
9
9
1
6/
1
/
1
9
9
2
6/
1
/
1
9
9
3
6/
1
/
1
9
9
4
6/
1
/
1
9
9
5
6/
1
/
1
9
9
6
6/
1
/
1
9
9
7
6/
1
/
1
9
9
8
6/
1
/
1
9
9
9
6/
1
/
2
0
0
0
6/
1
/
2
0
0
1
6/
1
/
2
0
0
2
6/
1
/
2
0
0
3
6/
1
/
2
0
0
4
6/
1
/
2
0
0
5
Ch
l
o
r
o
p
h
y
l
l

a

(
u
g
/
L
)
PIUTE RES AB DAM 01 PIUTE RES MIDWAY UP LAKE 02 PIUTE RES UPPER REACHES 03
Figure 2.2. Chlorophyll-a data for Piute Reservoir

2.4.7. Secchi Depth
Secchi depth is a measurement of surface water transparency and is measured by lowering a disk
with alternating black and white sections into the water. The secchi depth is the depth at which
the disk is no longer visible. High Secchi depth readings indicate that the water is relatively
clear and will allow sunlight to penetrate to greater depths than low readings, which indicate
turbid water.
Secchi depth measurements taken in Piute Reservoir since 1999 are summarized in Table 2.7 and
Figure 2.3. The table shows that values range from 0.3 meters to 5.0 meters with an average
depth of approximately 2.0 meters. Secchi depth measurements and how they relate to water
quality will be discussed in more detail in section 2.4.10.
The Secchi depths recorded for Piute Reservoir (Figure 3.9) show an increasing trend over time
during the summer growing season, in most cases. Data collected in 2006 are slightly lower than
in past years and are likely related to higher chlorophyll a values during this same sampling
period. Low secchi depth values also reflect non-algal turbidity associated with dissolved organic
carbon or carbonate alkalinity (Carlson 1992).

16
Table 2.7. Piute Reservoir Secchi Depth Summary.
Site Name Start End n
Min
(meters)
Average
(meters)
Max
(meters)
PIUTE RES AB DAM 01 7/5/2001 9/6/2005 6 0.4 2.3 4.0
PIUTE RES AB DAM 01 8/15/1979 9/14/1999 14 0.4 2.1 5.0
PIUTE RES MIDWAY UP
LAKE 02 7/5/2001 9/6/2005 6 0.3 2.0 4.1
PIUTE RES MIDWAY UP
LAKE 02 8/10/1989 9/14/1999 11 0.8 1.6 3.1
PIUTE RES UPPER
REACHES 03 7/5/2001 9/6/2005 6 0.9 1.7 2.6
PIUTE RES UPPER
REACHES 03 8/10/1989 9/14/1999 11 0.2 1.1 2.8

0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
6/
1
/
1
9
8
9
6/
1
/
1
9
9
0
6/
1
/
1
9
9
1
6/
1
/
1
9
9
2
6/
1
/
1
9
9
3
6/
1
/
1
9
9
4
6/
1
/
1
9
9
5
6/
1
/
1
9
9
6
6/
1
/
1
9
9
7
6/
1
/
1
9
9
8
6/
1
/
1
9
9
9
6/
1
/
2
0
0
0
6/
1
/
2
0
0
1
6/
1
/
2
0
0
2
6/
1
/
2
0
0
3
6/
1
/
2
0
0
4
6/
1
/
2
0
0
5
Se
c
c
h
i

D
e
p
t
h

(
m
e
t
e
r
s
)
PIUTE RES AB DAM 01 PIUTE RES MIDWAY UP LAKE 02 PIUTE RES UPPER REACHES 03
Figure 2.3. Secchi depth measurement for Piute Reservoir since 1999.
2.4.8. Water Column Data Assessment
This section discusses depth profile characteristics for dissolved oxygen, temperature, and pH as
well as an assessment of viable fish habitat. Depth integrated profile data for temperature, pH,
and dissolved oxygen collected by UDWQ were evaluated using the percentage-based criteria
established by the State of Utah specifically for dissolved oxygen. Depth integrated data are
available for the dam site, mid- reservoir site, and the upper reservoir site for the months shown
in Table 2.8. Additional profiles were also collected at each site in 1991, 1993, and 1997 and
were referenced to gain a historic perspective on profile trends.

17
Table 2.8. Depth Integrated Profile Sampling Frequency.
2001 2003 2005 2007
May
June x
July x x x
August x
September x

A summary of depth profile plots for dissolved oxygen, temperature and pH is displayed for all
Piute Reservoir sampling stations in Figure 2.4, Figure 2.5, and Figure 2.6. The figures
demonstrate the proportion of the sampled profiles with less than 4 mg/L dissolved oxygen,
temperature greater than 20 degrees C, as well as the percentage of the water column where State
water quality standards are met (Viable Habitat). As demonstrated in the figures (and Table 2.2),
dissolved oxygen below 4 mg/L occurs in much less than 50 percent of the water column.
Dissolved oxygen conditions are also typically better at the upper reservoir site (Figure 2.6) than
both the mid lake and dam sites, which is likely a result of shallower depths and complete mixing
from the wind and tributary inflows. The figures show that surface water temperature exceeds
the standard for the 3A beneficial use in most profile samples. As discussed in Section 2.4.4,
these exceedances were determined to be the result of natural solar radiation.

PIUTE RES AB DAM 01
54.6%
100.0%
6.5%6.7%
18.7%
26.4%
33.1%
5.7%
43.0%
65.4%60.2%
81.3%
67.9%
100.0%100.0%
2.4%
28.1%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7/5/2001 8/23/2001 6/15/2005 7/28/2005 8/10/2005 9/6/2005 7/5/2007 7/30/2007
%
W
a
t
e
r

C
o
l
u
m
n
Viable Habitat DO<4 mg/L Temp.>20 degC Figure 2.4. Depth Integrated Profile Summary for Piute Reservoir Above the Dam.

18
PIUTE RES MIDWAY UP LAKE 02
46.5%
59.8%
71.1%67.2%
100.0% 100.0%
8.6% 8.7%
100.0%
16.4%
31.6%
20.2%
46.5%
16.4%
7.0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7/5/2001 8/23/2001 6/15/2005 7/28/2005 8/10/2005 9/6/2005 7/5/2007 7/30/2007
%
W
a
t
e
r

C
o
l
u
m
n
Temp.>20 degC"Viable Habitat DO<4 mg/L Figure 2.5. Depth Integrated Profile Summary for Piute Reservoir at Mid-Lake.

PIUTE RES UPPER REACHES 03
75.0%75.8%80.6%
100.0%
8.6%
100.0% 100.0% 100.0%
24.2%19.4%16.4%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7/5/2001 8/23/2001 6/15/2005 7/28/2005 8/10/2005 9/6/2005 7/5/2007 7/30/2007
%
W
a
t
e
r

C
o
l
u
m
n
Temp.>20 degC"Viable Habitat DO<4 mg/L Figure 2.6. Depth Integrated Profile Summary for Piute Reservoir in the Upper
Reaches.

Figure 2.7, Figure 2.8, and Figure 2.9 present typical DO, pH, and temperature profiles during
critical summer conditions at the three reservoir sampling locations. The plots show surface of
the reservoir on top of the plot while depth increases down the vertical axis.
Figure 2.8 shows stratification occurring in the profile at the Dam Site and Mid-Reservoir Site,
respectively. A thermocline, the location in the profile where temperature changes by more than
1 oC within a 1 meter depth, occurs at 10 meters at the dam site and at 7 meters at the mid-
reservoir site. The thermocline in Piute Reservoir prevents mixing and allows the depletion of

19
dissolved oxygen in the lower depths of the reservoir as decomposition consumes oxygen from
the water column. Stratification in Piute Reservoir typically occurs in mid June when surface
water temperature increases and creates a sufficient thermal gradient throughout the profile to
prevent mixing. Stratification usually occurs between 7 to 10 meters deep and persists until late
July to mid-August. Mixing or fall turnover in the reservoir is primarily a function of reservoir
level and the occurrence of intense late summer thunderstorms. Once the reservoir is drawn
down to approximately 7 to 8 meters, the temperature throughout the water column is similar
enough to allow mixing to occur. Additionally, intense thunderstorms accompanied by high
winds provide sufficient wind energy to assist in mixing the water column.
Figure 2.9 shows typical profile conditions for the upper reservoir site. This site is usually
shallow enough to prevent summer stratification and is usually well mixed throughout the
profile. The well mixed profile is also a function of the site’s proximity to the reservoir inflow;
water movement from the inflow allows for physical mixing. Additionally, none of the current
or historical profiles at this location indicated DO depletion in the lower depths of the profile.

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
De
p
t
h

(
m
)
pH DO (mg/L)Temp (*C)
pH Std DO Min Std Temp Std
Figure 2.7. Typical Depth Integrated Profile Sample at the Dam Site During Critical
Conditions (7/28/2005).

20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
De
p
t
h

(
m
)
pH DO (mg/L)Temp (*C)
pH Std DO Min Std Temp Std
Figure 2.8. Typical Depth Integrated Profile Sample at the Mid-Reservoir Site During
Critical Conditions (7/28/2005).

0
1
2
3
4
5
6
7
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
De
p
t
h

(
m
)
pH DO (mg/L)Temp (*C)
pH Std DO Min Std Temp Std
Figure 2.9. Typical Depth Integrated Profile Sample at the Upper Reservoir Site During
Critical Conditions (7/28/2005).

21
2.4.9. Diurnal DO Data
Hourly depth integrated diurnal samples for temperature, DO, DO saturation, and pH are
available for a four day period from July 30, 2007 to August 3, 2007 at the Piute Reservoir dam
site. Samples were collected at 1.5 meters, 3.5 meters, 5.5 meters, and 7.5 meters, although
samples for the 1.5 meter location were lost due to equipment failure (Table 2.8). Total depth at
the site was 8.5 meters. Site observations during the sampling event include a visual observation
of a large algal bloom as well as frequent intense thunderstorms. Additionally, this sample was
collected approximately 2 weeks after de-stratification.
Table 2.8 demonstrates that values for the four parameters fluctuate with depth and through time.
Temperature throughout the profile for the entire sample period is above the 3A standard, but
generally decreases through time. Temperature also becomes more uniform throughout the
profile on 8/2/2007 due to influence of a large storm and wind mixing.
Dissolved oxygen concentration and saturation follow a similar trend as temperature. Assuming
that dissolved oxygen concentrations for the 1.5 meter sample (missing data) followed the same
trends as the 3.5 meter and 5.5 meter samples, greater than 50 percent of the water column had
concentrations greater the 4 mg/L. Both the 1.5 meter and 3.5 meter sample were determined to
be in the photic zone and diurnal oxygen fluctuations should be similar in both samples.
A noticeable exception occurred on 8/2/2007 where dissolved oxygen concentrations decreased
throughout the profile and less than 50 percent of the profile was above 4 mg/L. This
observation corresponds very well to the timing of a large storm and increased mixing of the
water column and is not a result of oxygen depletion from increased algal productivity and
nighttime respiration. Dissolved oxygen saturations are also low during this period and further
indicate that productivity was low. Therefore, the low dissolved oxygen concentrations in the
upper portion of the water column are most likely the result of mixing of surface waters with
bottom water containing low oxygen concentrations, which decreased oxygen concentrations
throughout the water column. Dissolved oxygen saturation is greater than 110 percent at various
times throughout the sampling period, which supports the visual observation of heavy algal
blooms at the beginning of the sampling period.
pH is relatively stable throughout the sampling period at all profile depths; however, values are
noticeably lower in the 7.5 meter sample. This difference is most likely due to the changes in
water chemistry as a result of low dissolved oxygen. The stability of values in the 3.5 meter
sample suggests that productivity does not influence pH during this sampling period.

22
0
1
2
3
4
5
6
7
8
9
7/30/07 12:00 7/31/07 0:00 7/31/07 12:00 8/1/07 0:00 8/1/07 12:00 8/2/07 0:00 8/2/07 12:00 8/3/07 0:00 8/3/07 12:00
DO

(
m
g
/
L
)
3.5 Meters 5.5 Meters 7.5 Meters 3A Standard
0
20
40
60
80
100
120
140
7/30/07 12:00 7/31/07 0:00 7/31/07 12:00 8/1/07 0:00 8/1/07 12:00 8/2/07 0:00 8/2/07 12:00 8/3/07 0:00 8/3/07 12:00
DO

S
a
t
u
r
a
t
i
o
n

(
%
)
3.5 Meters 5.5 Meters 7.5 Meters 3A Standard
20.0
20.5
21.0
21.5
22.0
22.5
23.0
23.5
7/30/07 12:00 7/31/07 0:00 7/31/07 12:00 8/1/07 0:00 8/1/07 12:00 8/2/07 0:00 8/2/07 12:00 8/3/07 0:00 8/3/07 12:00
Te
m
p

(
C
)
3.5 Meters 5.5 Meters 7.5 Meters 3A Standard
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
7/30/07 12:00 7/31/07 0:00 7/31/07 12:00 8/1/07 0:00 8/1/07 12:00 8/2/07 0:00 8/2/07 12:00 8/3/07 0:00 8/3/07 12:00
pH
3.5 Meters 5.5 Meters 7.5 Meters 3A Standard Figure 2.10. Diurnal Profile Data for the Piute Reservoir Dam Site.

23

2.4.10. Trophic State Index
Trophic state index (TSI) is a measurement of the biological productivity or growth potential of a
body of water. The basis for trophic state classification is an estimation of algal biomass present
in the water body. The calculation of a TSI generally includes the relationship between
chlorophyll, where chlorophyll a is used as a measure of algal biomass. Secchi depth and total
phosphorus TSI values are used as a surrogate to predict chlorophyll production. (Carlson and
Simpson 1996):
chlorophyll a: TSI CHL = 9.81 Ln (CHL) + 30.6
Secchi depth: TSI SD = 60– 14.41 Ln (SD)
total phosphorus: TSI TP = 14.42 Ln (TP) + 4.15
Oligotrophic water bodies have TSI values less than 30 and are generally transparent, have low
algal population densities, and have adequate dissolved oxygen throughout the water column
(Table 2.9). Mesotrophic water bodies with TSI values between 40-50 are moderately clear, and
have an increasing chance of hypolimnetic anoxia in summer. Eutrophic water bodies with TSI
values of 50–70) commonly experience more turbidity, higher algal population densities than
oligotrophic water bodies, low hypolimnetic dissolved oxygen levels in mid- to late-summer, and
often experience excessive macrophyte growth. Eutrophic water bodies are more supportive of
warm water fisheries than cold water fisheries. Hypereutrophic water bodies have TSI values
greater than 70, have heavy algal blooms, dense macrophyte growth, extensive dissolved oxygen
problems throughout the water column, and often have fish kills.
Table 2.9. Trophic State Index Categories.
TSI Trophic Status and Water Quality Indicators
< 30 Oligotrophic; clear water; high DO throughout the year in the entire hypolimnion
30–40 Oligotrophic; clear water; possible periods of limited hypolimnetic anoxia (DO =0)
40–50 Mesotrophic; moderately clear water; increasing chance of hypolimnetic anoxia in summer;
cold-water fisheries “threatened”; supportive of warm water fisheries
50–60 Mildly eutrophic; decreased transparency; anoxic hypolimnion; macrophyte problems; generally
supportive of warm-water fisheries only
60–70 Eutrophic: Blue-green algae dominance; scums possible; extensive macrophyte problems
70–80 Hypereutrophic: Heavy algal blooms possible throughout summer; dense macrophyte beds;
> 80 Hypereutrophic: Algal scums; summer fish kills; few macrophytes due to algal shading; rough
fish dominance
Source: From Carlson and Simpson, 1996.

Mean TSI values for Piute Reservoir are displayed in Table 2.10. TSI values for chlorophyll a
range from 42 at the mid-reservoir site to 45 at the dam site. Based on mean chlorophyll a
measurements, Piute Reservoir is classified as mesotrophic; however, total phosphorus and
secchi TSI values indicate the reservoir is mildly eutrophic. A discussion of these differences is
presented below. Figure 2.11, Figure 2.12, and Figure 2.13 display a temporal distribution of
TSI values for data collected since 1990. TSI values for each component do not show a

24
significant trend through time. Like mean TSI values, the figures also show that chlorophyll a
TSI values are lower than their secchi depth and total phosphorus counterparts in almost all
samples.
Table 2.10. Mean TSI Values in Piute Reservoir.
Site Name Chlorophyll a TSI Secchi Depth TSI Total Phosphorus TSI
Dam Site 45 52 54
Mid-Reservoir 42 54 57
Upper Reservoir 44 60 57

0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
19
9
0
19
9
1
19
9
2
19
9
3
19
9
4
19
9
5
19
9
6
19
9
7
19
9
8
19
9
9
20
0
0
20
0
1
20
0
2
20
0
3
20
0
4
20
0
5
20
0
6
TS
I
Chl TSI TP TSI SD TSI
Figure 2.11. Trophic State Index Trend Data for the Piute Reservoir Dam Site.

25
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
19
9
0
19
9
1
19
9
2
19
9
3
19
9
4
19
9
5
19
9
6
19
9
7
19
9
8
19
9
9
20
0
0
20
0
1
20
0
2
20
0
3
20
0
4
20
0
5
20
0
6
TS
I
Chl TSI SD TSI TP TSI Figure 2.12. Trophic State Index Trend Data for the Piute Reservoir Mid-Reservoir Site

0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
19
9
0
19
9
1
19
9
2
19
9
3
19
9
4
19
9
5
19
9
6
19
9
7
19
9
8
19
9
9
20
0
0
20
0
1
20
0
2
20
0
3
20
0
4
20
0
5
20
0
6
TS
I
SD TSI TP TSI Chl TSI Figure 2.13. Trophic State Index Trend Data for the Piute Reservoir Upper Reservoir
Site.
Determining the relationship between TSI values is helpful in identifying factors that limit algal
biomass. Although every water body is unique, a number of common relationships between
Secchi depth, chlorophyll a, and total phosphorus have been identified (Carlson and Simpson
1996). Figure 2.14, Figure 2.15, and Figure 2.16 display a multivariate comparison of each TSI
component. The following describes how to interpret the information presented in the plots.

26
Points plotting to the left of the vertical axis indicate reduced transparency from non-algal factors
including clay particles, dissolved organic matter, or reduced transparency resulting from
carbonate alkalinity (Carlson 1992). Points to the right of the vertical axis indicate transparency
is greater than predicted by chlorophyll TSI, which can occur when large particulate matter like
blue-green algae or other organic matter dominate. Additionally, in situations where chlorophyll
TSI is under predicted by phosphorus TSI (points plotting below the horizontal axis), something
other than phosphorus is limiting chlorophyll abundance, whereas points above this axis indicate
that chlorophyll production is limited by phosphorus concentrations. The diagonal line
extending from the lower left quadrant to the upper right quadrant indicate the level of agreement
between secchi depth TSI and total phosphorus TSI. Points plotting to the left of the origin
indicate situations where TP and sechhi depth are well correlated, but chlorophyll is not.
The routine occurrence of chlorophyll a TSI values less than secchi depth and total phosphorus
TSI values are as depicted in Figure 2.14, Figure 2.15, and Figure 2.16. These figures indicate
that chlorophyll production is limited by something other than phosphorus availability, turbidity
is reduced due to suspended particulates rather than chlorophyll a, and that chlorophyll is under-
predicted by both secchi depth and phosphorus.
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60
Increasing
phosphorus
Surplus
Increasing
phosphorus
Limitation
TSI chl > TSI SD
TS
I

C
h
l

>

T
S
I

T
P

T
S
I

C
h
l

<
T
S
I

T
P
Small Particulates Large Particulates
Zooplankton
Grazing
Non-Algal
Turbidity
TSI chl < TSI SD
Dissolved
Color/Clay
Particles
Figure 2.14. TSI Relationships for the Piute Reservoir Dam Site.

27
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60
Increasing
phosphorus
Surplus
Increasing
phosphorus
Limitation
TSI chl > TSI SD
TS
I

C
h
l

>

T
S
I

T
P

T
S
I

C
h
l

<
T
S
I

T
P
Small Particulates Large Particulates
Zooplankton
Grazing
Non-Algal
Turbidity
TSI chl < TSI SD
Dissolved
Color/Clay
Particles
Figure 2.15. TSI Relationships for the Piute Reservoir Mid-Reservoir Site.

-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
-60-50-40-30-20-100 102030405060
Increasing
phosphorus
Surplus
Increasing
phosphorus
Limitation
TSI chl > TSI SD
TS
I

C
h
l

>

T
S
I

T
P

T
S
I

C
h
l

<
T
S
I

T
P
Small Particulates Large Particulates
Zooplankton
Grazing
Non-Algal
Turbidity
TSI chl < TSI SD
Dissolved
Color/Clay
Particles
Figure 2.16. TSI Relationships for the Piute Reservoir Upper Lake Site.

2.4.11. Fishery Management

The Utah Division of Wildlife Management (DWR) manages Piute Reservoir as a put and take
fishery for rainbow trout and small mouth bass. Water levels play a significant role in the

28
viability of the reservoir’s trout fishery (UDWR, 2006). On average, Piute Reservoir is nearly
drained one out of every six years, which makes maintaining a long term fishery difficult.
Additionally, when reservoir levels remain high for more than a few years, trout populations are
inhibited by increasing competition with nongame species. DWR can easily remove nongame
fish during periods with low reservoir levels, but if water levels remain high, it is not
economically feasible. As a result, DWR is establishing a small mouth bass population to
improve fishing conditions during periods with low water levels and elevated nongame
competition. However, DWR maintains that when reservoir water levels are optimal, trout
populations thrive and fishing conditions are some of the best in the state (UDWR, 2006).
No fish kills have been reported in Piute Reservoir (DEQ 2008).
2.4.12. Phytoplankton composition
The presence of blue-green algae, or cyanobacteria, has been associated with the occurrence of
toxins and mortality in local animal populations. Although cyanobacteria may be of low
toxicity, cyanotoxins can become concentrated in the environment or through bioaccumulation
where cyanobacterial growth occurs. Cyanobacteria can dominate nitrogen-limited systems due
to their ability to fix atmospheric nitrogen. As a result, cyanobacteria can increase where low
nitrogen limits the growth of other algal species (Sharpley et al. 1984, 1995; Tiessen 1995).
The relative densities of algal species and diversity of the algal community both serve as
surrogate measures of water quality by identifying overall species diversity, excessive algal
growth or eutrophication, and the presence and relative abundance of toxic blue-green algae.
Detailed plankton data are available for the dam site at Piute Reservoir for September 14, 1999
and August 23, 2001 (Rushforth and Rushforth 2000, Rushforth and Rushforth 2002). Algal
taxa present at these times were identified and grouped by taxon to show green algae
(chlorophyta), blue-green algae (cyanophyta), diatoms (bacillariophyta) and others.
In the 1999 and 2001 sampling, green algae dominated at 49.3% and 53.1 % relative density,
respectively, of the total algal population. Diatoms represented a smaller population at 11.3%
and 46.9%, respectively of the total. Blue-green algae were not detected in 2001; however, a
population was present in 1999, representing 37.0% of the total phytoplankton population.
2.4.13. Existing Watershed TMDLs
The watershed contributing to Piute Reservoir consists of two major drainages; the East Fork
Sevier River and the Sevier River. Both watersheds have EPA approved TMDLs in place for
total phosphorus. The TMDL endpoint for these watersheds is an in-stream total phosphorus
concentration of 0.05 mg/L, which equates to a 45 percent reduction and a 55 percent reduction
for the East Fork Sevier River and the Sevier River, respectively.
Current flow, total phosphorus concentrations, and load conditions for the East Fork Sevier River
and The Sevier River at Kingston, UT are presented in Figure 2.17, Figure 2.18, and Figure 2.19.
The figures demonstrate that Piute Reservoir receives approximately 60 percent of its inflow
from the Sevier River, most of which is delivered between October and June. The East Fork
Sevier River delivers the majority of summer volume to the reservoir via water release from
Otter Creek Reservoir (Figure 2.17).
Total phosphorus concentrations are generally higher in the Sevier River inflow than the East
Fork Sevier River except during the summer months. Lower phosphorus concentrations and
flow during the summer in the Sevier River are the result of a complete upstream diversion for
irrigation use. (Figure 2.18).

29
Figure 2.18 and Table 2.11 demonstrate that of the 17,805 kg/yr total phosphorus delivered to
Piute Reservoir, approximately 65 percent (11,617 kg/year) is from the Sevier River. The East
Fork Sevier River delivers the majority of the summer load for an annual total of approximately
6,188 kg/year (35 percent of the total load).
0.0E+00
1.0E+08
2.0E+08
3.0E+08
4.0E+08
5.0E+08
6.0E+08JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecemberAv
g
e
r
a
g
e

D
i
s
c
h
a
r
g
e

(
f
t
^
3
)
Sevier River @ Kingston E.F. Sevier River @ Kingston Figure 2.17. Average Total Monthly Inflow to Piute Reservoir.

0.00
0.05
0.10
0.15
0.20
0.25JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecemberTo
t
a
l

P
h
o
s
p
h
o
r
u
s

(
m
g
/
L
)
Sevier River @ Kingston E.F. Sevier River @ Kingston
Figure 2.18. Average Monthly Inflow Total Phosphorus Concentrations

30
Figure 2.18 and Table 2.11 also demonstrate the effect of expected phosphorus reductions into
Piute Reservoir as a result of upstream TMDLs for total phosphorus. When the upstream TMDL
targets are achieved, total phosphorus load to the reservoir is expected to be reduced from 17,805
kg/year to 8,515 kg/year for a load reduction of approximately 48 percent. This load reduction is
expected to significantly decrease in-reservoir total phosphorus concentrations.
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
2,200
2,400
2,600JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecemberTo
t
a
l

P
h
o
s
p
h
o
r
u
s

L
o
a
d

(
k
g
)
Sevier R. @ Kingston E.F. Sevier R. @ Kingston
Sevier R. @ Kingston Load Capacity E.F. Sevier R. Load Capacity Figure 2.19. Average Total Monthly Total Phosphorus Load and Loading Capacity.

31
Table 2.11. Average Total Phosphorus Load and TMDL Targets.
Current Conditions Expected Load Reductions

Sevier R. @
Kingston
E.F. Sevier R.
@ Kingston
Total to
Piute
Reservoir
Sevier R.
@
Kingston
E.F.
Sevier
R.
Piute
Reservoir
Month TP (kg)
%
Total
TP
(kg)
%
Total TP (kg) TP (kg) TP (kg) TP (kg)
January 1,280.1 88.7% 162.9 11.3% 1,443.1 563.3 89.6 652.9
February 1,101.0 83.2% 222.8 16.8% 1,323.8 484.5 122.5 607.0
March 2,077.3 87.1% 307.2 12.9% 2,384.5 914.0 169.0 1,083.0
April 631.6 57.5% 466.9 42.5% 1,098.6 277.9 256.8 534.7
May 966.8 38.6% 1,540.1 61.4% 2,506.9 425.4 847.1 1,272.5
June 2,531.1 73.5% 911.8 26.5% 3,442.8 1,113.7 501.5 1,615.1
July 82.9 6.1% 1,280.5 93.9% 1,363.4 36.5 704.3 740.8
August 105.6 14.0% 649.4 86.0% 755.0 46.5 357.2 403.6
September 117.2 24.5% 360.7 75.5% 477.9 51.6 198.4 250.0
October 322.3 76.9% 96.7 23.1% 419.0 141.8 53.2 195.0
November 1,242.4 91.1% 121.0 8.9% 1,363.3 546.6 66.5 613.2
December 1,158.6 94.4% 68.3 5.6% 1,226.8 509.8 37.6 547.3
Total 11,616.9 65.2% 6,188.3 34.8% 17,805.2 4,976.9 3,403.6 8,515.0

Significant BMP implementation efforts are already in progress in both watersheds and include
stream bank restoration and re-vegetation, riparian exclusion, off stream stock watering, and
range improvement practices. The effects of these projects are expected to be evident in the
short-term, while full realization of environmental benefits will occur through long-term
implementation efforts.

32
3.0 WATER QUALITY SUMMARY
3.1. Compliance with Water Quality Criteria
No observed exceedances of the 3A dissolved oxygen criteria have occurred in Piute Reservoir
and more than 50 percent of the water column meets dissolved oxygen criteria of > 4.0 mg/L
during all months at the three reservoir sites. Chlorophyll a values were also supportive of
literature recommendations for support of coldwater fisheries with only 6.8 percent of the
observations exceeding the recommended concentration. Additionally, no pH exceedances
occurred in the dataset and detailed analysis revealed that pH does not respond to productivity,
suggesting that algal productivity is not excessive in the reservoir.
3.2. Explanation of Exceedances
3.2.1. Total Phosphorus
Total phosphorus concentrations at all sampling locations in the reservoir routinely exceed the
State’s indicator value of 0.025 mg/L. However, elevated phosphorus concentrations do not
appear to influence productivity to an extent to cause depletion of dissolved oxygen through
decomposition of organic matter and respiration during the night. As discussed in the evaluation
of TSI values in section 2.4.10, this is likely the result of particulate-bound phosphorus
unavailable for algal growth.
3.2.2. Temperature
Results of a reservoir heat budget conducted by the Utah Division of Water Quality determined
that temperature impairment to the cold water fishery in Piute Reservoir is due to natural solar
radiation and significant decreases would not be obtained by implementation of best
management practices (BMPs). Piute Reservoir was removed from the 303(d) list based on the
results of this analysis.
3.2.3. Diurnal Profile Sampling
Some observations in the diurnal dataset were low enough to deplete DO in more than 50 percent
of the water column; however, an analysis of climatalogical data during the sampling period
indicated that low dissolved oxygen was the result from normal reservoir mixing rather than
elevated productivity. The occurrence of DO depletion occurs simultaneously with an intense
storm event. The storm event combined with shallow reservoir depths made mixing of surface
and bottom water possible. Bottom water containing low dissolved oxygen concentrations
mixed with surface water and effectively lowered surface oxygen concentrations. This mixing is
considered a natural event for reservoirs of this nature. The influence of decreased dissolved
oxygen with mixing is not expected to persist and surface water concentrations will gradually
increase back to normal.
3.3. Trophic State
Analysis of the trophic state of Piute Reservoir indicates the reservoir is generally mesotrophic.
Occurrences of reduced turbidity measured in terms of secchi depth generally indicate a non-
algal source of light interference most typically associated with fine particulates. Additionally,
phosphorus is generally unavailable for algal production and supports the conclusion that total
phosphorus concentrations above the 0.025 mg/L indicator value are not adversely affecting the
health of the fishery.

33
3.4. Watershed TMDLs
EPA approved TMDLs are in place and currently in the implementation phase for both the
Sevier River and East Fork Sevier River watersheds. These watersheds are the primary inflows
to the reservoir and watershed wide BMP implementation will further improve water quality
conditions in Piute Reservoir. The combined result of these TMDLs is expected to translate into
an approximate 48 percent reduction of total phosphorus into the reservoir. With current water
quality conditions fully supporting the cold water fishery beneficial use in Piute Reservoir,
additional phosphorus removal provides assurance of long term beneficial use support.

34
References
Carlson, R.E. 1992. Expanding the trophic state concept to identify non-nutrient limited lakes
and reservoirs. pp. 59-71 [In] Proceedings of a National Conference on Enhancing the
States’ Lake Management Programs. Monitoring and Lake Impact Assessment. Chicago.
Carlson, R.E. and J. Simpson. 1996. A Coordinator’s Guide to Volunteer Lake Monitoring
Methods. North American Lake Management Society. 96 pp.
Pilgrim, K., D. Sanders, and T. Dupuis. 2001. Relationship between chlorophyll a and beneficial
uses. CH2M Hill, Boise, Idaho. 10 p.
Sharpley, A.N.; Hedley, M.J.; Sibbesen, E.; Hillbricht-Ilkowska, A.; House, W.A.; Ryszkowski,
L.; 1995; Phosphorus transfers from terrestrial to aquatic ecosystems; Chapter 11, In
Phosphorus in the Global Environment: transfers, cycles and management; Tiessen,
H.(ed.); John Wiley and Sons, Chichester.
Sharpley, A.N.; Jones, C.A.; Grey, C.; Cole, C.V.; 1984; A simplified soil and plant phosphorus
model II: Prediction of labile, organic and sorbed phosphorus; Soil Science Society of
America Journal; Volume 48; pp 805-809.
Tiessen, H. (ed.); 1995; Phosphorus in the Global Environment: Transfers, Cycles and
Management; Scientific Committee on Problems of the Environment (SCOPE) 54; John
Wiley and Sons, Chichester.
Utah Division of Water Quality (UDWQ), Department of Environmental Quality. 2007. Lake
report: Piute Reservoir. URL:
http://www.waterquality.utah.gov/watersheds/lakes/piute.pdf. [viewed 1/25/2008].
Utah Division of Wildlife Resources (UDWR), Utah Department of Natural Resources. 2006.
The cycle is up and so is the number and size of fish at Piute Reservoir. URL:
http://wildlife.utah.gov/news/06-06/piute.php. [Viewed 2/8/2008].