Notice to Avoid and Report Possible Harmful Cyanobacteria Blooms (HCBs) in Wyoming Waters
Wyoming Department of Environmental Quality sent this bulletin at 05/13/2026 08:00 AM MDT
Notice to Avoid and Report Possible Harmful Cyanobacteria Blooms (HCBs) in Wyoming Waters
CHEYENNE, WYOMING - With summer upon us and more people heading to Wyoming’s lakes and reservoirs to recreate, the Wyoming Department of Environmental Quality (WDEQ), the Wyoming Department of Health (WDH), and the Wyoming Livestock Board (WLSB), in collaboration with partners, remind the public to avoid and keep animals away from harmful cyanobacteria blooms (HCBs) and report suspected blooms and bloom-related illnesses to the WDEQ and WDH at WyoHCBs.org.
Cyanobacteria, also called blue-green algae, can form harmful blooms (HCBs) that produce cyanotoxins and other irritants, posing risks to human and animal health. HCBs usually appear in mid-to-late summer and can occur in streams, rivers, lakes, and reservoirs. HCBs can vary in appearance – they may be green, tan, brown, or blue-green, and can float in or on the water. They often look like spilled paint, clumps, grass clippings, or scum. HCBs may stick to underwater surfaces like rocks, plants, or debris, appearing as films or mats that are often chunky or slimy, which could detach and float to the surface or collect along the shoreline.
If a bloom is present, the WDH and WLSB recommend the following:
Avoid contact with water in and around the bloom, especially in areas where cyanobacteria are dense.
Do not swallow water from the bloom. Boiling, filtration, 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.
Seek medical attention or a veterinarian if a person or animal is sick after exposure to a cyanobacteria bloom. Young children, pregnant women, people with weakened immune systems, and animals are at higher risk. Information on health risks and symptoms related to a cyanobacteria bloom can be found on WDH’s webpage: https://health.wyo.gov/publichealth/infectious-disease-epidemiology-unit/disease/harmful-algal-blooms/.
The WDH follows up on all HCB illness reports, and the WDEQ will investigate potential blooms to determine if they are harmful. As outlined in Wyoming's HCB Action Plan, the WDH will issue advisories for waterbodies where cyanobacteria or toxins may pose a risk to people who come into contact with the water. A Bloom Advisory is issued for a waterbody when a cyanobacteria bloom is present and cyanotoxins may be present. A Toxin Advisory is issued for a particular location within a waterbody when toxin concentrations exceed safe recreational levels. A webmap of current and past advisories and answers to frequently asked questions (FAQs) can be found at WyoHCBs.org. Since there may be additional waterbodies with cyanobacteria blooms of which the WDH and WDEQ are not aware, it is important to check the water for signs of blooms even when there is no advisory for the waterbody.
For more information, visit Wyoming’s HCB webpage at WyoHCBs.org.
