DWQ-2025-003104

Utah Benthic Cyanobacteria
Advisory Guidance
Last updated: April 1, 2025
Version 1.5
This guidance was drafted by a workgroup of partners from the Utah Department of
Environmental Quality (DEQ), Utah Department of Health and Human Services (DHHS),
Local Health Departments (LHDs), Utah State Parks (DNR), Bureau of Land Management
(BLM), and the National Park Service (NPS).
This guidance is anticipated to be issued jointly by DEQ and DHHS to provide guidance for
LHDs and other agencies managing public recreational water bodies affected by toxigenic
benthic cyanobacteria mats (harmful algae mats). While dogs and other animals will be
referenced in communication and educational materials, this guidance is designed to be
protective of human health.
Benthic cyanobacteria basics
Toxin-producing benthic cyanobacteria mats, colloquially referred to as harmful algae mats,
have been identied in 27 Utah waterbodies since targeted DEQ data collection began in
2020. Benthic cyanobacteria mats may produce dangerous toxins, known as cyanotoxins,
that can harm people, pets, livestock, and wildlife. These mats have been linked to
numerous human illnesses and multiple dog deaths in Utah.
Benthic cyanobacteria mats grow in both owing and standing water such as rivers, creeks,
reservoirs, ponds, lakes, and canals, where they adhere to submerged rocks, plants, sand,
and banks. Mats may also detach and oat on the water surface, accumulate in eddies, or
wash up on shore.
Exposure routes
Exposure to cyanotoxins generally occurs when an individual comes into direct contact with
a mat through dermal contact or ingestion. Dogs and children are most likely to come in

direct contact with mat material. Dogs and other animals may be attracted to the musty
smell and purposefully seek out and eat benthic mats.
Disturbed or naturally detaching mats pose high recreational risk as they are more likely to
be incidentally ingested by recreators than mats attached to the benthos. Benthic
cyanobacteria mats are buoyant and often accumulate in slow-moving areas of water, like
swimming holes or along shorelines. Benthic mats may also release toxins into the overlying
water column that may be incidentally ingested by recreators swimming or engaging in
waterplay.
Recreators ltering drinking water in the backcountry also experience increased risk. No
commercially available backcountry lter has been shown to effectively remove
cyanotoxins. Exposure may occur if benthic cyanobacteria are present in the water used for
ltering.
Adverse health eects
Thus far, anatoxin is the cyanotoxin most commonly detected in association with benthic
cyanobacteria mats in Utah. Anatoxins are potent neurotoxins that can harm the nervous
system. At low to moderate doses of exposure, anatoxin causes neurologic symptoms
including muscle twitching, tingling, numbness, salivation, and loss of balance. At high
doses, anatoxin may cause rapid death from respiratory paralysis (EPA, 2024). Sixty-two
percent of Utah benthic samples containing a species from order Oscillatoriales have
had detectable anatoxin production.
Other cyanotoxins, including microcystin, nodularin, cylindrospermopsin, and saxitoxin,
may be produced by Utah benthic cyanobacteria species. Even in the absence of toxins,
there are signicant associations between cyanobacteria cells and adverse health effects
including gastrointestinal illness and dermal irritation (EPA, 2019).
Individuals who believe they may be experiencing symptoms of exposure should contact
the Utah Poison Control Center (UPCC) at 1-800-222-1222. UPCC data are relayed to the
Centers for Disease Control and Prevention and help expand our knowledge about
cyanobacteria, cyanotoxins, and their adverse health effects.
Benthic mat monitoring
Benthic cyanobacteria mats can be green, yellow, brown, or black. They often have a
mucousy, gelatinous texture and earthy odor. Mats may grow in lakes, ponds, puddles,
wetlands, ditches, canals, hot springs, creeks, and rivers and may not be obvious without
careful inspection. DEQ maintains a webpage with photos to aid identication. There is no
way to determine if a mat is toxic just by looking at it. Lab analysis is required to identify

and quantify cyanotoxin presence.
Evaluating human health risk
Unlike planktonic cyanobacterial blooms (harmful algal blooms), exposure risk to benthic
cyanobacteria mats cannot be quantied by toxigenic cell density or toxin concentration
from samples taken from the water column. Both cyanobacteria cells and cyanotoxins are
contained in dense concentrations in the mat matrix, while the surrounding undisturbed
water has little to no detectable cells or toxins. Consequently, existing state and federal
guidelines for planktonic cyanobacteria cannot be directly applied in evaluating human
health risk from benthic cyanobacteria.
Furthermore, it is challenging to evaluate cyanotoxin production in benthic cyanobacteria
mats. Toxic and non-toxic mats can co-occur within feet of each other (Wood et al., 2010).
Additionally, the ratio of toxic to non-toxic cells composing a mat may change in a matter of
days to weeks – e.g., a mat that was non-detect for toxins one week, may be producing
toxins the next (Wood et al., 2012; Valdez-Cano et al., 2023). The specic cyanotoxins
produced by benthic species is also an area of emerging research with analytical limitations
and no federal guidelines for interpreting in-mat toxin concentrations. Mat toxin
concentration may not directly relate to exposure risk. Consequently, while toxin data can
help rene risk assessment, toxin concentration alone cannot currently provide a reliable
basis for benthic-specic advisory issuance.
As a result of these factors, using benthic cyanobacteria mat percent coverage is the
most common global metric for evaluating human health risk (New Zealand Ministry for
the Environment, 2009; ITRC, 2021; California Water Boards, in prep.) and the best precedent
available for Utah to follow.
High coverage of benthic cyanobacteria increases the likelihood of a recreator coming into
contact with mats and potential cyanotoxins. The location of benthic mats may also
increase recreational risk: for example, mats accumulating near a popular beach, oating in
an enclosed lentic system, or highly concentrated at a popular soak spot are much more
likely to result in human exposure.
The taxa of benthic cyanobacteria present also inuences which cyanotoxins may be
produced (e.g., Rosen & St. Amand, 2015; California Water Boards, 2020). In Utah, detected
toxin production has almost always been associated with benthic cyanobacteria belonging
to the order Oscillatoriales, including genera Microcoleus, Tychonema, Phormidium, and
Oscillatoria. Human illnesses and dog deaths in Utah have likewise been linked to this
taxonomic order. As a result, the following guidance is focused on benthic cyanobacteria of
the order Oscillatoriales. Toxin production and exposure risk in other known
toxin-producing benthic genera is the subject of on-going research in the State of Utah.

Sampling procedures
A statewide collaborative workgroup has established recreational water quality sampling
procedures for benthic cyanobacteria. See the DEQ “Benthic Percent Coverage SOP.”
Coverage evaluation is made using a point intercept method. Measuring cover by points has
long been a standard practice in plant ecology (Jonasson, 1988; Elzinga et al., 2015) for both
terrestrial and aquatic cover (UK Environmental Change Network, 1999; Necchi et al., 1995).
Point intercept methods have been shown to be less biased and more objective than line
intercepts or visual estimates in plots or quadrats (Bonham, 1989; Godínez-Alvarez et al.,
2009). Point intercept methods are also faster than many alternative coverage methods and
require only basic supplies and training (Madsen & Wersal, 2012). This combination results
in an approach that yields quantiable results, while also being accessible to monitoring
partners around the state (US EPA, 2024).
Cyanotoxin samples may also be collected to help rene risk assessment, but are not a
required component of the guidance recommendation. A sample for cyanotoxins will
represent a composite of 8 to 10 separate mats in order to average the effect of spatial
variability.
Benthic cyanobacteria monitoring is generally conducted by DEQ staff, local health
departments, or land-managing agencies.
Interpreting results
This procedure is designed to assess human health risk in recreational use areas where
benthic cyanobacteria mats are present. No additional action is recommended when no
visible benthic cyanobacteria are present. Educational signage is recommended when low
coverage (<20%) of benthic cyanobacteria are present. A formal Warning Advisory is
recommended when high coverage (≥20%) of benthic cyanobacteria are present or mats pose
high recreational risk (Table 1). A Warning Advisory may also be recommended in instances
where benthic cyanobacteria coverage is expected to reach/exceed 20% or pose high
recreational risk before the next feasible monitoring visit. The 20% threshold was selected
based on the precedent set by New Zealand in their benthic cyanobacteria monitoring work
(New Zealand, 2009). This threshold may be adjusted as additional targeted research
becomes available.
Table 1. Qualiers for high recreational risk and descriptions.
High risk qualifier Description
Cyanobacteria mats accumulating on the shore Mats that have become detached are accumulating

along the shoreline or on the shore. This includes both
wet and dried mats
Floating cyanobacteria mats Floating mats are observed in stagnant areas or floating
downstream while surveying
Enclosed lentic systems Enclosed lentic systems
The waterbody being assessed is a small pond or other
enclosed lentic system. Any disturbed/detached mats
are likely to come in contact with potential recreators

Recreational contact with mats likely Mat placement and/or size such that mats are likely to
come into contact with potential recreators
Current guidance is written specically for benthic cyanobacteria species belonging to the
order Oscillatoriales. While other toxigenic species may be present in Utah, our state
currently lacks the data to appropriately evaluate their human health risk. Educational
signage and consultation with DEQ and DHHS is recommended for waterbodies with high
coverage of benthic cyanobacteria belonging to other taxonomic orders (e.g., Nostocales).
In unusual circumstances where established benthic cyanobacteria mats are not expected to
be producing toxins, weekly to biweekly toxin testing may be used to downgrade a warning
advisory to educational signage.
Public communication and advisories
The statewide workgroup has established a two-tier approach to public health
communication and advisory action for benthic cyanobacteria. Recommended actions rely
on evaluation of mat coverage and recreational risk factors.
Table 2 summarizes the recommended public health actions.
Authority
In Utah, the authority to post health advisories and close water bodies lies with the local
health departments. DHHS and DEQ provide support and data to these local partners.
A local health department may:
● Prepare, publish, and disseminate information necessary to inform and advise the
public concerning the health and wellness of the population, specic hazards, and
risk factors. – Utah Code 26A-1-114 (1)(i)(i)

● Close theaters, schools, and other public places and prohibit gatherings of people
when necessary to protect public health. – Utah Code 26A-1-114 (1)(e)
Other land managing agencies, such as the National Park Service, Bureau of Land
Management, and US Forest Service, may also choose to issue advisories or post educational
signage.
Advisory guidance thresholds
Table 2. Advisory guidance thresholds for Utah recreational waters affected by benthic
cyanobacteria.
Post Educational Signs Issue Warning Advisory
Benthic cyanobacteria mats Present A Present A
High recreational risk 1,2 Not present Present B
Benthic mat coverage (%) 1,2 <20% ≥20% C, D
Recommended actions
This is not a formal advisory level, but
rather an education-focused response
to anticipated recreational risk

Post educational signage

Follow-up monitoring is highly
recommended
Issue WARNING advisory. Recreators
should avoid activities that could
lead to ingestion of mat material

Post WARNING advisory signage

Follow-up monitoring is highly
recommended. Consider toxin
testing
A This guidance is specifically for benthic cyanobacteria belonging to the order Oscillatoriales (includes common Utah genera:
Microcoleus, Tychonema, Phormidium, and Oscillatoria). For waterbodies with toxigenic benthic cyanobacteria of other orders (e.g.,
Nostocales), educational information should still be posted. Consult with DHHS/DEQ for further risk assessment.
B High recreational risk includes mats accumulating on the shoreline; floating mats; small, enclosed lentic systems; and sites
where recreational contact with mats is likely.
C A Warning Advisory may be merited in instances where benthic cyanobacteria coverage is expected to reach/exceed 20% or
pose high recreational risk before the next feasible monitoring visit. Consult with DEQ/DHHS as needed.
D In unusual circumstances where established mats are not expected to be producing toxins, regular toxin testing may be used to
downgrade a warning advisory to educational information. Consult with DHHS/DEQ.
1 New Zealand, 2009. New Zealand Guidelines for Cyanobacteria in Recreational Fresh Waters
2 ITRC, 2021. Strategies for Preventing and Managing Harmful Cyanobacterial Blooms HCBs)

Advisory guidance process
Figure 1. Flowchart showing a typical process for monitoring and responding to benthic
cyanobacteria in a recreational water body.

1 This guidance is specifically for benthic cyanobacteria belonging to the order Oscillatoriales (includes common Utah genera:
Microcoleus, Tychonema, Phormidium, and Oscillatoria). For waterbodies with toxigenic benthic cyanobacteria of other orders (e.g.,
Nostocales), educational information should still be posted. Consult with DHHS/DEQ for further risk assessment.
2 Atypically high recreational risk includes mats accumulating on the shoreline; floating mats; small, enclosed lentic systems; and
sites where recreational contact with mats is likely.
3 In unusual circumstances where established mats are not expected to be producing toxins, regular toxin testing may be used to
downgrade a warning advisory to educational information. Consult with DHHS/DEQ.

Contact information
Report benthic cyanobacteria mats: UDEQ 24-hour Spill Hotline: [phone]
Immediate health concerns: Utah Poison Control Center: 1-800-222-1222
Human illness information: Utah Poison Control Center: 1-800-222-1222
Animal illness information: ASPCA Animal Poison Control Center*: 855-764-7661
Pet Poison Control Helpline*: 801-536-4123
*There is often a $90-100 fee for these calls.
Utah Division of Water Quality: [phone]; habs.utah.gov
● Hannah Bonner, [e-mail]
● Ben Holcomb, [e-mail]
Utah Department of Health & Human Services: [phone]; website
● Alejandra Maldonado, [e-mail]
● Karen Valcarce, [e-mail]
References
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California Water Boards, 2020. Freshwater cyanotoxin producers chart. Available online at:
https://drive.google.com/le/d/1VNnBPYiE4XIoy6xyFXgYEiW7dBgV47Y-/view?usp=sharing
California Water Boards, in preparation. Benthic cyanobacteria guidance.
Elzinga, C.L., Salzer, D.W., Willoughby, J.W., 2005. Measuring & Monitoring Plant Populations. Bureau of Land
Management, Denver, CO, BLM Technical Reference 1730-1.
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https://www.epa.gov/sites/default/les/2019-05/documents/hh-rec-criteria-habs-document-2019.pdf
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https://neiwpcc.org/wp-content/uploads/2024/11/USHAB12_Full-Abstract-Book.pdf
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