Editor's Note Aug 20, 2025: This article was updated to include three new toxin advisories in Guernsey and Pathfinder Reservoirs and McKenzie Lake.
Six waterbodies are under toxin advisories for having harmful cyanobacteria blooms (HCB).
They include Diamond Lake (Bolser) northwest access, Guernsey Reservoir at Sandy Point campground, Leazenby Lake south access, McKenzie Lake dog park shore, and Pathfinder Reservoir at Bishops point ramp and Woodruff Narrows north ramp. A toxin advisory is issued for a waterbody when toxin concentrations exceed recreational use thresholds, according to the state Department of Environmental Quality.
Thirty-one Wyoming lakes and reservoirs are under advisories for having potentially harmful cyanobacteria blooms (HCB).
The state issues a bloom advisory for a water body 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.
The blooms are caused by imbalances of nutrients in the water and warm temperatures. Alerts tend to rise in the summer.
Blooms and toxins may only be present in certain areas of a waterbody and conditions can change frequently.
Blooms have been identified at:
- Alcova Lake
- Boysen Reservoir
- Brooks Lake
- Diamond Lake (Bosler Reservoir)
- Flaming Gord Reservoir
- Fontenelle Reservoir
- Glendo Reservoir
- Goshen Hole Reservoir
- Grayrocks Reservoir
- Guernsey Reservoir
- Hawk Springs Reservoir
- High Savery Reservoir
- Leazenby Lake
- Little Soda Lake
- Lower North Crow Reservoir
- Luckey Pond
- Miller Lake
- McKenzie Lake
- Ocean Lake
- Pathfinder Reservoir
- Pelham Lake
- Rainbow Lake
- Saratoga Lake
- Sloans Lake
- Upper Brooks Lake
- Viva Naughton Reservoir
- Wheatland Reservoir #1
- Wheatland Reservoir #3
- Woodruff Narrows Reservoir
Weste DuNoir Creek near Murray Lake is currently under investigation as testing results are pending.
Cyanobacteria, also called blue-green algae, can form blooms that produce cyanotoxins and other irritants that pose risks to human and animal health. The blooms 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 also stick to underwater surfaces like rocks, plants or debris, appearing as films, mats or jelly-like balls.
If you, a pet or livestock touches the algae, rinse off with clean water as soon as possible. This water is not ok to drink, even if boiled or filtered. Seek medical attention if you or your furry friend gets sick after exposure.
The CDC lists symptoms of ingestion of cyanotoxins as headache, fever, bloody or dark urine, nausea, vomiting or diarrhea.
Young children, pregnant women, people with weakened immune systems and animals are at higher risk. More information on health risks and symptoms related to a cyanobacteria bloom can be found on the Wyoming Health Department’s webpage.
The Health Department and Wyoming Livestock Board recommend:
- 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.
Other waterbodies in the state may also be affected. New or questionable blooms can be reported to WyoHCBs.org or WyoSpills.org.
