Harmful Cyanobacterial Blooms


Sampling Resources

Educational Materials

Wyoming Action Plans and Materials for Management Agencies


Chloe Schaub
Recreational Water Quality
Program Coordinator

Courtney Tillman,
Surveillance Epidemiologist

Hallie Hasel
State Veterinarian

Harmful cyanobacterial blooms (HCBs) are dense concentrations of cyanobacteria (photosynthetic single-celled microscopic organisms) that pose a health risk to people and animals. Cyanobacteria are commonly referred to as blue-green algae because they look very similar to algae. For this same reason, HCBs are commonly referred to as harmful algal blooms or HABs.

What do HCBs look like?

Under normal conditions, cyanobacteria are present in surface waters at low levels and play an important role in aquatic ecosystems. When HCBs occur, cyanobacteria become visibly abundant and can look like grass clippings, blue-green scum, or spilled paint on the water surface. HCBs may also be suspended in the water column or attached to rocks, sediments, or aquatic plants. To view photos of harmful cyanobacterial blooms found in Wyoming, click here

How can I tell the difference among cyanobacteria, non-toxic algae and aquatic plants?

Individual cyanobacterial cells are small but can cluster together to form scums or mats. Because cyanobacterial scums or mats are comprised of individual cells, they can be broken-up when disturbed. Algae often form long hair-like networks that cling together when disturbed. Aquatic plants are generally much larger than cyanobacteria, grow attached to the bottom of a waterbody, and have extensive stem, leaf, and root networks. The Department of Environmental Quality (DEQ) has provided easy tests to distinguish between cyanobacteria and algae in the resources section of this webpage.

Why are cyanobacterial blooms harmful?

Cyanobacteria can produce toxins and other irritants that can cause several health effects in people and animals, including pets and livestock. People and animals can be exposed to cyanobacteria and their associated toxins and irritants via skin contact with water or bloom material, breathing in water spray, or ingesting water or bloom material. Health effects include rashes, itching, numbness, fatigue, disorientation, abdominal pain, vomiting, and diarrhea. In extreme cases, cyanotoxins may lead to wildlife, pet or livestock death. Blooms may also cause fish kills due to depleted oxygen levels, create issues for drinking water supplies and agriculture, and lead to tourism and property value losses. To find more information on HCB-related health effects for people and animals, visit the Center for Disease Control and Prevention’s webpage.

How can I keep people and animals safe?

Check to see which waterbodies have a BLOOM ADVISORY, TOXIN ADVISORY, or are UNDER INVESTIGATION on the HCB Advisories in Wyoming Waters webmap. Keep in mind that there may be waterbodies with HCBs that the Wyoming Department of Health is not aware of. Also, keep in mind that waterbodies with an advisory are not closed since HCBs may only be present in certain areas and conditions can change frequently.

If you encounter a potential HCB, the Wyoming Department of Health and the Wyoming Livestock Board recommend the following:

  • Avoid contact with water in the vicinity of the bloom, especially in areas where cyanobacteria are dense and form scums.
  • Do not ingest water from the bloom. Boiling, filtration and/or other treatments will not remove toxins.
  • Rinse fish with clean water and eat only the fillet portion.
  • Avoid water spray from the bloom.
  • Do not allow pets or livestock to drink water near the bloom, eat bloom material, or lick fur after contact.
  • If people, pets, or livestock come into contact with a bloom, rinse off with clean water as soon as possible and contact a doctor or veterinarian.

Practices to protect animals and people from HCBs by restricting access to contaminated water or providing alternative water sources are outlined on the Natural Resources Conservation Service webpage.

How can I report a potential HCB?

Report the suspected HCB to the Department of Environmental Quality (DEQ) at 307-777-7501 or by clicking “Submit a Complaint” on the Report a Spill webpage, WyoSpills.org, so DEQ can investigate.

What should I do if people or animals get sick or come into contact with a HCB?

Rinse off with fresh water and contact a doctor or veterinarian. Report HCB related illnesses to the Wyoming Department of Health. The Wyoming Poison Control Center can be reached at 1-800-222-1222.

As summarized in Wyoming’s HCB Response Strategy, when a HCB is reported on a waterbody without a current recreational use advisory and the report is determined to be credible, the waterbody will be identified as “Under Investigation” on the HCB Advisories in Wyoming Waters webmap. If the Department of Environmental Quality (DEQ) verifies that a HCB is present at the waterbody, the Wyoming Department of Health (WDH) will issue a BLOOM ADVISORY.

If resources are available, DEQ will collect samples to determine the amount of cyanobacteria present and the concentrations of cyanotoxins present. If cyanobacteria abundance or cyanotoxin concentrations are above public health thresholds, the WDH will retain the BLOOM ADVISORY, issue a new BLOOM ADIVSORY if one has not been issued, or issue a TOXIN ADVISORY.

How long are HCB Advisories in effect?

Once the Wyoming Department of Health (WDH) issues a TOXIN ADVISORY for a waterbody, it will be in effect until two cyanotoxin samples, collected at least 1-day apart, are below the recreational-use levels identified in in the Wyoming HCB Action Plan or December 31st, whichever comes first. BLOOM ADVISORIES remain in effect until blooms have dissipated, as indicated by visual evidence, cyanobacteria densities below the recreational-use levels, or December 31st, whichever comes first.

How is satellite imagery being used to monitor HCBs?

The Department of Environmental Quality (DEQ) analyzes satellite imagery from the Cyanobacteria Assessment Network (CyAN) for the presence of cyanobacterial blooms on an approximately weekly basis. The CyAN imagery provides an estimate of cyanobacterial cell densities in approximately 40 lakes and reservoirs in Wyoming due to the unique spectral signature of cyanobacteria. DEQ analyzes satellite imagery for these waterbodies using screening metrics that identify the areal extent of blooms, cyanobacteria cell density, and bloom persistence over time.

Does DEQ test waterbodies on private land for HCBs?

The Department of Environmental Quality (DEQ) does not provide sampling or analytical services for waterbodies on private land. Private landowners interested in sampling a potential cyanobacterial bloom can utilize DEQ’s standard operating procedures for cyanotoxin and cyanobacteria sample collection and EPA’s list of commercial cyanobacteria and cyanotoxin laboratories.



What causes HCBs?

Cyanobacteria occur naturally in surface waters, both in the water column as part of the phytoplankton community or attached to substrates such as rocks, sediment, wood, aquatic vegetation, or other surfaces as part of the periphyton community. HCBs that develop in the water column (i.e., planktonic HCBs) most commonly occur in still or slow-moving surface waters, such as lakes and reservoirs. HCBs that develop attached to surfaces form biofilms or mats (i.e., mat-forming HCBs) and are most common in wadable streams and rivers but can also be found in lakes, reservoirs, and hot springs. Mat-forming HCBs can detach, move downstream, and float to other locations in a waterbody. Wind can also aggregate cyanobacteria. Factors such as sunlight, water clarity, nutrients (e.g., phosphorus and nitrogen), carbon, water velocity and mixing, water temperatures, and consumption by other aquatic organisms can affect the formation of planktonic and mat-forming HCBs. Planktonic HCBs often form in waterbodies with excess nitrogen and phosphorus. Mat-forming HCBs can occur in waterbodies with limited nutrient availability because the cyanobacteria can access nutrients from the substrates and algae, microbes, and inorganic matter that is present within the mat matrix. Nitrogen and phosphorus can enter surface waters from fertilizers, animal waste from pets and livestock, wastewater from treatment plants and septic systems, detergents, stormwater runoff, cars, and fuel-burning power plants.

Is there a way to clean up or remove HCBs?

There are a number of practices that can prevent, disrupt, and dissipate HCBs. The Interstate Technology Regulatory Council (ITRC) has recently compiled strategies for preventing and managing harmful cyanobacterial blooms. Because cyanobacteria are naturally occurring and heavily influenced by environmental factors, strategies to clean up or remove HCBs should consider the site-specific characteristics and uses of each waterbody. Strategies to clean up or remove HCBs must also be mindful of the potential for treatments to release toxins into the environment.

In cases where nitrogen and phosphorus pollution is contributing to the formation of HCBs, reducing the amount of nitrogen and phosphorus that enters surface waters may be the best long-term solution to prevent HCBs from occurring.

What other efforts are underway to address HCBs in Wyoming?

Since HCBs are a water quality issue and can be caused by excess nutrients, the Department of Environmental Quality (DEQ) has partnered with the Wyoming Nutrient Work Group, a stakeholder group comprised of agencies, organizations, and members of the public, to develop the Wyoming Nutrient Strategy. The strategy identifies priority items and next steps for addressing nutrient pollution through development of water quality criteria for nutrients, reducing nutrients from point sources and nonpoint sources of pollution, and educating the public about nutrient pollution and its effects on Wyoming’s waters.


DEQ is also collaborating with researchers at the University of Wyoming’s Department of Zoology and Physiology to better predict and manage HCBs that occur within the state. This research has helped to inform the effectiveness of satellite imagery to identify and quantify HCBs in lakes and reservoirs and evaluate the prevalence of blooms in lakes and reservoirs over the last 35 years. Research is also underway to identify environmental conditions that may contribute to HCBs, including the role of nutrients in specific waterbodies, and improve understanding of cyanotoxin production and monitoring.   

What can I do to minimize HCBs?
  • Report problems when you find them to the Department of Environmental Quality’s (DEQ’s) spill and complaint site. This will ensure that the Department of Environmental Quality (DEQ) is aware of problem areas.
  • Report illnesses to the Wyoming Department of Health.
  • Participate in the Wyoming Nutrient Work Group and help provide DEQ with input on how to most effectively address nutrient pollution.
  • Be aware of potential contributions from your own home; use the recommended amount of fertilizer on your lawn, use phosphorus-free detergents, fix leaky septic systems, and pick up pet waste.
  • Additional information is available through the Interstate Technology Regulatory Council and the Environmental Protection Agency.

The Wyoming Department of Health (WDH) asks that you report human and animal illnesses that may have been caused by bloom exposure on WDH’s Harmful Cyanobacteria Reporting page. Information reported to WDH will help WDH, DEQ, and collaborators understand how many people and animals become sick from HCBs each year, the potential symptoms associated with HCBs-related illnesses, and where HCBs and illnesses occur in Wyoming. The WDH will report any individual human or animal cases of HCB-related illness to the One Health Harmful Algal Bloom System (OHHABS), a collaborative for local and state health officials to report and track illnesses.

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