Gem State Roundup

Health advisories issued for Hells Canyon, Brownlee reservoirs in Idaho

By: - August 3, 2023 4:46 pm
Cyanobacteria water

Cyanobacteria blooms occur when blue-green algae rapidly grows out of control. (Courtesy of Lorraine Backer/Centers for Disease Control and Prevention public health image library)

Idaho Department of Health and Welfare officials are urging the public to avoid drinking and direct contact with the water at the popular Hells Canyon Reservoir and Brownlee Reservoir areas due to harmful algal blooms. 

The Idaho Department of Health and Welfare issued the health advisories after water samples from both areas came back with high amounts of toxin-producing cyanobacteria, department officials announced in a press release issued Thursday.

Summer heat can cause dangerous conditions, harmful algal blooms in Idaho’s rivers and lakes


Hells Canyon Reservoir is located in Adams County, and Brownlee Canyon is located in Washington County. Both flow into the Snake River and are popular fishing spots. 

Idaho Department of Health and Welfare officials are urging people to stay out of the water, keep their pets and livestock away from the water and avoid drinking and cooking with the water. 

Symptoms in people include a rash, hives, nausea, diarrhea, vomiting, wheezing and red eyes. Health officials warned that animals and pets can become very sick and die within minutes to days of exposure to cyanotoxins. If pets or animals come in contact with water from a harmful bloom, the animal should be washed with clean water immediately and prevented from licking cyanobacteria off their body or fur. If an animal is exposed to cyanobacteria and starts to appear sick, health officials urge the public to seek veterinary care immediately.

The algal blooms may look like surface scum, foam, spilled paint, foam or a mat. Health officials said cyanobacteria are a natural part of Idaho’s waters, but the amount of bacteria increases when water temperatures rise and there are nutrients for the bacteria to bloom.

Additional information is available online. The Idaho Department of Health and Welfare said it will advise the public when the harmful conditions likely no longer exist.


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Clark Corbin
Clark Corbin

Clark Corbin has more than a decade of experience covering Idaho government and politics. He has covered every Idaho legislative session since 2011 gavel-to-gavel. Prior to joining the Idaho Capital Sun he reported for the Idaho Falls Post Register and Idaho Education News. His reporting in Idaho has helped uncover a multimillion-dollar investment scam and exposed inaccurate data that school districts submitted to the state.