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.

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.
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.
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.
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.
Rinse off with fresh water and contact a doctor or veterinarian. The Wyoming Poison Control Center can be reached at 1-800-222-1222.
If the bloom consists of harmful cyanobacteria, the Department of Environmental Quality (DEQ) will collect samples to determine if cyanotoxins and/or the amount of cyanobacteria are at unsafe levels. If unsafe levels are present, DEQ will notify the Wyoming Department of Health (WDH) so an Advisory can be issued. If signage is not already present at a waterbody, resource management agencies or local officials will post signs around the waterbody that include recommendations on how to keep people and animals safe. DEQ maintains a webmap with active Advisories and will send notices to interested persons via an email listserv. For more information on Advisories, click here.
Once the Wyoming Department of Health (WDH) issues an Advisory, it will be in effect until the bloom dissipates and cyanotoxin concentrations fall below harmful levels or the primary contact recreation season ends on September 30th, whichever comes first. The primary contact recreation season (May 1 – September 30) is used for HCB Advisories because this is the period when surface water and air temperatures are conducive to swimming and similar water contact activities and therefore HCBs pose the greatest health risks to people. HCBs often persist beyond the primary recreation season, however, and recreationists should continue to be aware of potential health risks for people, pets, and livestock.
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.
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 sample collection and EPA’s list of commercial cyanobacteria and cyanotoxin laboratories.
Cyanobacterial blooms are most commonly caused by excessive amounts of nitrogen and phosphorus from fertilizers, animal waste from pets and livestock, wastewater from treatment plants and septic systems, detergents, stormwater runoff, cars, and fuel-burning power plants. In addition, shallow water with abundant sunlight, warm temperatures, still or slow moving water, can also cause cyanobacteria to grow rapidly. Wind may also concentrate cyanobacteria.
Although reducing nutrient pollution is the best long-term solution to prevent HCBs from occurring, there are a number of additional practices that can disrupt and dissipate HCBs. DEQ is currently participating in a national work group to compile information on these practices.
The Department of Environmental Quality 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 numeric nutrient criteria, reducing nutrients from point sources and nonpoint sources, and educating the public about nutrient pollution and its impacts.
  • Report problems when you find them. This will ensure that the Department of Environmental Quality (DEQ) is aware of problem areas.
  • 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.
The Wyoming Department of Health (WDH) will report any individual human or animal cases of HCB-related illness using the One Health Harmful Algal Bloom System (OHHABS). Currently, OHHABS is a collaborative for state and federal partners that allows local and state health officials to report and track illnesses.