Toxic Algae in Wyoming

Who tracks blooms in Wyoming

Wyoming calls these blooms harmful cyanobacterial blooms, or HCBs. The Wyoming Department of Environmental Quality (DEQ) investigates reports and collects samples when it can, and screens EPA satellite imagery about once a week. Its program focuses on public water used for swimming and other full body contact.

The Wyoming Department of Health (WDH) issues advisories and takes illness reports, and the Wyoming Livestock Board recommends precautions for animals.

Bloom advisories and toxin advisories

Under the state’s HCB Action Plan, a Bloom Advisory is based on cyanobacteria at or above 20,000 cells per milliliter, and a Toxin Advisory is triggered by microcystins at or above 8 micrograms per liter or cylindrospermopsin at or above 15 micrograms per liter, among other toxins.

Water under an advisory is not closed, because blooms can be patchy and change quickly. It is up to you to avoid the bloom.

Check before you go

• The Wyoming DEQ HCB page links the current advisory map and recent bloom photos.
• Look at the water. Scum, paint like streaks and green flecks are reasons to stay out even with no advisory posted. See what a bloom looks like.

How to report a bloom or illness in Wyoming

• Call the DEQ spill and complaint line at (307) 777-7501.
• Use the online HCB report form at deqspills.wyo.gov.
• Report an illness in a person or animal through WDH’s online harmful cyanobacteria survey, linked from the DEQ page.
• For a possible poisoning, call the Wyoming Poison Control Center at (800) 222-1222.

Keeping people, pets and livestock safe

• Avoid contact with water near a bloom, especially dense scum, and avoid spray from it.
• Do not drink bloom water. The state notes that boiling, filtering and other treatments will not remove the toxins.
• Rinse fish with clean water and eat only the fillet.
• Keep pets and livestock from drinking near a bloom, eating bloom material or licking their fur after contact.
• After any contact, rinse with clean water as soon as you can and call a doctor or vet if needed.

EPA swimming advisory values

The US Environmental Protection Agency recommends a swimming advisory whenever microcystins are above 8 micrograms per liter or cylindrospermopsin is above 15 micrograms per liter on any single day. Wyoming’s toxin advisory levels for microcystins and cylindrospermopsin match EPA’s.

You cannot tell whether a bloom is making toxins by looking at it, and toxin levels can change from one week to the next. Only a lab test can tell you what is in the water.

Private and ranch lakes

DEQ suggests that private landowners follow its sampling procedures and use a commercial lab. Our algae ID and cyanotoxin analysis identifies the algae and tests for toxins, and we serve lakes across western Wyoming from our Eagle, Idaho office.

Sources, checked November 4, 2026. Wyoming DEQ, Harmful Cyanobacterial Blooms. Wyoming HCB Action Plan (2021 update). US EPA, Protecting Human Health from Cyanotoxin Exposure During Recreation. US EPA, Recreational criteria and swimming advisories for microcystins and cylindrospermopsin (2019).