The Idaho Department of Health and Welfare issued a health advisory Monday for Brownlee and Hells Canyon reservoirs after water samples revealed elevated levels of toxin-producing cyanobacteria in both bodies of water.
The same warning was extended earlier this month to Crane Creek Reservoir in Washington County, which also tested positive for high concentrations of the harmful microorganism. All three reservoirs are now under active advisory.
What the Advisory Means for Recreation
Residents and visitors are urged to avoid direct contact with the water in all three reservoirs. State health officials emphasized the risk to both humans and animals, recommending that people “evaluate water conditions before swimming, boating, or letting pets enter any lake or reservoir.”
Consumption of water from these reservoirs is strongly discouraged. Neither boiling nor standard filtering removes the toxins produced by cyanobacteria, making the water unsafe for drinking or cooking regardless of treatment method.
Fishing remains permitted, though the state recommends careful hand-washing after handling fish and thorough cleaning before consumption.
Health Risks and Symptoms
Contact with cyanobacteria-contaminated water can trigger skin rashes, hives, gastrointestinal distress, and headaches in humans. Pets face accelerated health risks and should be washed immediately after exposure to the water.
Cyanobacteria blooms may be visible as mats, foam, or surface scum, though the organisms can be present even when no discoloration appears on the water’s surface.
Why This Happens in Summer
Rising temperatures during the warmer months trigger increased cyanobacteria proliferation. The microorganisms are naturally occurring in Idaho watersheds but flourish when conditions favor their growth. The harmful algal bloom season extends throughout the summer months, with risk declining as temperatures drop in fall.
The state continues to monitor water conditions at the three affected reservoirs. Residents are encouraged to check with local health departments or the Department of Health and Welfare for updated advisories as conditions change.
For additional information on wildfire activity in the region, see coverage of the Greer Fire and Highway 11 closures.