Harmful Cyanobacterial Blooms


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Kelsee Hurshman
Watershed Protection Surface Water Quality HCB 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 at low levels and play an important role in aquatic ecosystems. When HCBs occur, cyanobacteria become visibly abundant 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 plants on the bottom of the waterbody. 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 cyanobacteria are small and do not form long, filamentous networks. Cyanobacteria can cluster together to form scums or mats, but these can be broken up when disturbed. Algae often form long, hair-like networks that cling together. Aquatic plants are generally much larger, attach to the bottom of the water body, and have extensive stem and leaf networks. 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. 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. More information on HCB-related health effects for people and animals: Center for Disease Control and Prevention.

What should I do if I suspect a 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. If DEQ has not yet investigated a bloom, the Wyoming Department of Health and Wyoming Livestock Board recommend the following:

  • Avoid contact with the water in the vicinity of the bloom, especially in areas where cyanobacteria are dense and form scrums.
  • 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.

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.

Wyoming’s HCB Action Plan Flow Chart summarizes the events that occur when HCBs and HCB related illnesses are reported.

If a HCB or HCB related illness is reported in a waterbody without a history of HCBs and the report is determined to be credible, the waterbody will be identified as “Under Investigation” on the HCBs Advisories in Wyoming Waters webmap. If a HCB or HCB related illness is reported in a waterbody with a history of HCBs and the presence of a bloom is verified with photographs, videos, or satellite imagery, the WDH will issue a BLOOM ADVISORY.


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, or issue a TOXIN ADVISORY.

How long are HCB Advisories in effect?

Once the Wyoming Department of Health (WDH) issues an Advisory for a waterbody, it will be in effect until the bloom dissipates and cyanotoxin concentrations fall below levels identified in the Wyoming Harmful Cyanobacterial Bloom Public Health Notification Levels for Recreational Waters. For visual confirmation that a bloom has dissipated, the Department of Environmental Quality (DEQ) reviews photographs and videos of the bloom site, and satellite imagery, if available.

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 can currently detect HCBs 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?

Cyanobacterial blooms most commonly occur in still or slow-moving surface waters with abundant sunlight, warm temperatures, and excess amounts of nitrogen and phosphorus. Wind may also concentrate cyanobacteria. 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?

Although reducing the amount of nitrogen and phosphorus that enters surface waters is the best long-term solution to prevent HCBs from occurring, there are a number of additional practices that can disrupt and dissipate HCBs. The Interstate Technology Regulatory Council (ITRC) has recently compiled strategies for preventing and managing harmful cyanobacterial blooms.

What other efforts are underway to address HCBs in Wyoming?

Since HCBs are a water quality issue and often 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 to 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 impacts.


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 will help inform the effectiveness of satellite imagery to identify and quantify HCBs, help identify environmental conditions that may lead to a HCB, and identify management methods to prevent future HCBs.

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 illness 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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