DWQ-2025-004874

Implementation of cyanotoxin criteria for recreational uses in Utah
June 12, 2025

Executive summary
In 2019, the U.S. Environmental Protection Agency (EPA) issued recommended water
quality criteria for two cyanotoxins: microcystins and cylindrospermopsin. The
recommended criteria are designed to protect the public from incidental exposure to
harmful levels of these cyanotoxins while participating in recreational water-contact
activities in freshwater where immersion and incidental ingestion of water are likely. For
microcystins, the EPA recommended recreational water quality criterion value is 8
micrograms (μg)/liter (L). For cylindrospermopsin, the EPA recommended recreational
water quality criterion value is 15 μg/L.
Utah’s water quality standards include protections for two recreational use classes,
frequent primary contact recreation, which includes activities like swimming, rafting,
kayaking, diving, and water skiing, and infrequent primary contact recreation, which
includes activities like wading, shing, and hunting.
DWQ has reviewed the recommendations and determined that adopting these criteria for
Utah’s frequent primary contact use class will enhance protections for recreators in Utah
surface waters.
Utah cyanotoxin criteria • Implementation document 2 of 9

Introduction
Background
Many species of cyanobacteria can produce cyanotoxins that can harm people, pets,
livestock, and wildlife. Cyanotoxins that have been found in Utah waters include
microcystins, cylindrospermopsin, saxitoxins, and anatoxins. Exposure to cyanotoxins
may cause short-term or long-term human illness and has been known to kill pets and
wildlife. Elevated cyanotoxin concentrations are associated with harmful algal blooms
(HABs). HABs occur when naturally occurring cyanobacteria quickly multiply to high
densities and form visible water discoloration, scums, or mats. HABs are most likely to
form in water bodies with high nutrient levels and ecological disturbance.
In 2019, the U.S. Environmental Protection Agency (EPA) issued recommended water
quality criteria for two cyanotoxins: microcystins and cylindrospermopsin (Environmental
Protection Agency 2019a). The criteria were developed to protect human health from
recreational exposure to cyanotoxins. Utah’s water quality standards include protections
for two recreational use classes, frequent primary contact recreation, which includes
activities like swimming, rafting, kayaking, diving, and water skiing, and infrequent
primary contact recreation, which includes activities like wading, shing, and hunting.
Utah is obligated by federal regulations to review the recommended criteria and, if
appropriate, update Utah’s criteria to include the recommendations. DWQ has reviewed the
recommendations and determined that adopting these criteria will enhance protections for
recreators in Utah surface waters.
EPA recommended criteria
● For microcystins, the EPA recommended recreational water quality criteria value is 8
micrograms (μg)/liter (L).
● For cylindrospermopsin, the EPA recommended recreational water quality criteria
value is 15 μg/L.
While other cyanotoxins (e.g., saxitoxins and anatoxins) and toxigenic cell density are
included in many state and global guideline frameworks cited in the 2019 document, the
EPA has not released recommended criteria for these indicators at this time.
Utah cyanotoxin criteria • Implementation document 3 of 9

The values for microcystins and cylindrospermopsin are based on episodic, short-term
exposure of recreating children. For use as a recreational water quality criterion, the EPA
recommends a maximum of three excursions across a recreational season and observation
of that pattern across more than one year to reect seasonal dynamics and occurrence
patterns of HABs (Table 1). The recommended criteria are designed to protect the public
from incidental exposure to harmful levels of these cyanotoxins while participating in
recreational water-contact activities in freshwater where immersion and incidental
ingestion of water are likely (Environmental Protection Agency 2019b). Such activities
include, but are not limited to, swimming, water skiing, tubing, skin diving, water play by
children, or similar water-contact activities in waterbodies designated for such
recreational uses.
Table 1. EPA recreational water quality criteria for microcystins and cylindrospermopsin
Microcystins Cylindrospermopsin
Magnitude
(μg/L)
Duration Frequency Magnitude
(μg/L)
Duration Frequency
8
1 in 10-day
assessment
period across
a recreational
season
More than 3
excursions in a
recreational season,
not to be exceeded in
more than one year*
15
1 in 10-day
assessment
period across
a recreational
season
More than 3
excursions in a
recreational season,
not to be exceeded in
more than one year*
* An excursion is dened as a 10-day assessment period with any toxin concentration higher than the criteria
magnitude. When more than three excursions occur within a recreational season and that pattern reoccurs in
more than one year, it is an indication the water quality has been or is becoming degraded and is not supporting
its recreational use.
Cyanotoxins in Utah
DWQ has been actively monitoring HABs and cyanotoxins in Utah surface waters since
2014. As of 2024, HABs have been observed in at least 43 recreational lakes or reservoirs in
Utah. These blooms often include toxinogenic cyanobacteria, and cyanotoxins including
microcystins, cylindrospermopsin, saxitoxins, and anatoxins have been measured. Blooms
are monitored, quantied, and communicated by a collaborative statewide program. Local
Health Departments may issue recreational advisories in response to elevated levels of
cyanotoxins or toxigenic cell counts.
Microcystins are the cyanotoxin for which Utah currently has the most monitoring data. In
monitoring from 2021-2024, microcystins were detected in 46% of analyzed HAB samples
Utah cyanotoxin criteria • Implementation document 4 of 9

with a median detection of 2.89 μg/L. In monitoring from 2016-2024, 289 recreational
samples (28% of analyzed samples) have detected microcystins at or above 8 μg/L.
Cylindrospermopsin has been less frequently observed in Utah. Cylindrospermopsin was
detected in 18% of analyzed HAB samples from 2021-2024 with a median detection of 0.09
μg/L. No analyzed samples in Utah to date have exceeded 15 μg/L of cylindrospermopsin.
Four waterbodies in Utah have exceeded the EPA recreational water quality criteria for
microcystins (Table 1) for at least one year since routine data collection began: Mantua
Reservoir, Big East Lake, Utah Lake, and Panguitch Lake. Seventeen Utah waterbodies
were listed as impaired for HABs in Utah’s 2024 Integrated Report due to cyanotoxin
concentrations or recreational limitations due to the presence of HABs.
Recommended criteria
Magnitude, duration, and frequency
DWQ recommends adopting numeric criteria for microcystins of 8 ug/L and
cylindrospermopsin of 15 ug/L as recommended by EPA (2019) to Utah’s water quality
standards for waters classied as category 2A, frequent primary contact recreation use.
Utah’s frequent primary contact recreation use includes activities with a high likelihood of
incidental water ingestion and a high degree of bodily contact with water such as
swimming, rafting, kayaking, diving, and water skiing. This use class directly corresponds
to the recreational activities that the recommended criteria were developed to protect;
water-contact activities in freshwater where immersion and incidental ingestion of water
are likely.
The criteria should also be applied programmatically where the existing use of a
waterbody includes frequent primary contact uses, even if that waterbody is currently
classied in rule as a 2B infrequent primary contact water. Class 2B waters where frequent
primary contact uses are identied as an existing use should be reclassied to class 2A.
DWQ also recommends adopting the recommended duration and frequency of EPA (2019).
An excursion is dened as one cyanotoxin concentration exceeding the criterion
magnitude in a 10-day assessment period. Three excursions within a recreational season
constitutes an exceedance of the criterion, and the criterion is not to be exceeded in more
than one year.
Utah cyanotoxin criteria • Implementation document 5 of 9

Proposed rule language
R317-2-14. Numeric Criteria.
TABLE 2.14.1
NUMERIC CRITERIA FOR DOMESTIC,
RECREATION, AND AGRICULTURAL USES

Domestic Recreation and Agri-
Parameter Source Aesthetics culture
1C(1) 2A 2B 4
BACTERIOLOGICAL
(30-DAY GEOMETRIC
MEAN) (NO.)/100 ML) (7)
E. coli 206 126 206

MAXIMUM
(NO.)/100 ML) (7)
E. coli 668 409 668

CYANOTOXINS (ug/L) (8)
Microcystins 8
Cylindrospermopsin 15

FOOTNOTES:
(8) An excursion is defined as a 10-day assessment period with any toxin concentration higher than the criterion magnitude. More
than 3 excursions in a recreational season not to be exceeded in more than one year.
Implementation considerations
Sampling and analytical methods
DWQ’s HAB monitoring SOP (UDWQ 2024) recommends that monitoring for HABs and
cyanotoxins, “target areas where there is a reasonable maximum risk of human-cyanotoxin
interaction and exposure.” This is consistent with the recommendations in EPA 2019b to,
“target sample collection toward capturing the highest potential exposure risks,” by
collecting samples from swimming areas, shorelines, and within splash zones where
children play. DWQ’s HAB program routinely collects both surface (1-2 inch depth) and
depth integrated (elbow depth) samples for cyanotoxins. Surface samples are only
collected when algal blooms have formed a concentrated algal scum. In these instances,
risk of ingestion of surface water from common recreational activities like swimming,
children playing in the shallows, or spray from jet- and water-skiing, may be captured.
Depth integrated samples are generally also separately collected and evaluated any time a
cyanotoxin sample is collected. EPA 2019a and 2019b do not make specic
recommendations regarding sample depth for cyanotoxins. DWQ’s evaluation of both
Utah cyanotoxin criteria • Implementation document 6 of 9

surface and depth integrated samples in targeted recreation areas ensures that DWQ
monitoring captures the highest potential exposure risk. Per EPA 2019b, while samples
collected within target areas may be composited, samples collected over different days
within a ten-day assessment period should not be averaged.
The recommended criteria do not require any specic analytical methods for cyanotoxins.
However, analytical methods should be sufficiently sensitive and have minimum detection
limits lower than criteria magnitudes. DWQ’s HAB program uses enzyme-linked
immunosorobent assay (ELISA) to quantify total microcystins and cylindrospermopsin.
These methods are consistent with EPA’s recommendations. ELISA for microcystins has a
detection limit of 0.3 µg/L and provides a measure of the sum of all microcystin congeners.
ELISA for cylindrospermopsin has a detection limit of 0.15 µg/L.
Water quality assessments
As of Utah’s 2024 Integrated Report, cyanotoxin assessment methods are consistent with
the recommended criteria magnitudes, frequencies, and durations. An impairment for
cyanotoxins is identied when more than three excursions, dened as a cyanotoxin
concentration exceeding the recommended criteria in a 10 day assessment period, occur in
a recreational season in more than one year. Current cyanotoxin assessment methods do
not specically dene a recreational season.
No substantive changes to the assessment methods are required by adoption of the
recommended cyanotoxin criteria, but future assessment methods should consider
updates to dene the recreational season and clarify the use of additional indicators. E.
Coli assessment methods dene a general recreational season of May 1 through October 31
with an allowance for adjustment on a site-specic basis. The same denition may be
appropriate for cyanotoxin assessments. Following criteria adoption, cyanotoxin
assessment methods can be moved from the narrative standard assessment to the numeric
criterion assessment section. Both harmful algal bloom and E. Coli assessment methods
separately incorporate an evaluation of recreational health advisories and closures. Future
assessment method updates should consider consolidating all recreational health advisory
based assessments into a single, narrative standard based assessment method and aligning
duration and frequency components for health advisory evaluations with the
recommended cyanotoxin criteria.
Recreational advisory program
Adopting the recommended cyanotoxin criteria will not require any specic changes to the
advisory program. Utah’s recreational advisory program already recommends advisory
Utah cyanotoxin criteria • Implementation document 7 of 9

issuance at recommended microcystin and cylindrospermopsin concentrations. Similar to
many programs acknowledged in EPA 2019a, the recreational advisory program also
leverages other indicators of human health risk to make advisory decisions, including
additional cyanotoxins and toxigenic cell counts.
Permiing
The cyanotoxin criteria will not result in any direct impacts to permits as no permittees
discharge cyanotoxins. However, impairments for cyanotoxins and HABs in general could
result in more stringent nutrient effluent limits following the development of TMDLs or site
specic nutrient criteria. Potential costs associated with these criteria are inestimable
because impairment determinations are currently unknown, potential TMDL endpoints or
numeric nutrient criteria would be site specic, and nutrient treatment options will be
discharger specic.
Utah cyanotoxin criteria • Implementation document 8 of 9

References
Environmental Protection Agency. 2019a. “Recommended Human Health Recreational
Ambient Water Quality Criteria or Swimming Advisories for Microcystins and
Cylindrospermopsin.” Recreational Water Quality Criteria and Methods.
https://www.epa.gov/wqc/recreational-water-quality-criteria-and-methods.
Environmental Protection Agency. 2019b. “Final Technical Support Document:
Implementing the 2019 National Clean Water Act Section 304(a) Recommended
Human Health Recreational Ambient Water Quality Criteria or Swimming Advisories
for Microcystins and Cylindrospermopsin.” Recreational Water Quality Criteria and
Methods.
https://www.epa.gov/wqc/recreational-water-quality-criteria-and-methods.
Utah Division of Water Quality. 2024. “Standard Operating Procedure For Sample
Collection And Identication Of Harmful Algal Blooms.” Quality Assurance and
Quality Control Program: Water Quality Monitoring.
https://deq.utah.gov/water-quality/quality-assurance-and-quality-control-program-
monitoring-water-quality.
Utah cyanotoxin criteria • Implementation document 9 of 9