Health advisories for Idaho water bodies lifted as winter approaches

December 1, 2025

Author DHW Communications The Department of Health and Welfare (DHW) has lifted health advisories for water bodies affected by cyanobacterial harmful algal blooms (cyanoHABs) but continues to urge caution when recreating in or near the water.

DHW collaborates with the Idaho Department of Environmental Quality (DEQ) and local public health districts to identify, respond to, and monitor cyanoHABs. DEQ monitors and samples for cyanoHABs when risk to recreationists is high. Conditions that support toxic blooms significantly diminish with cooler temperatures, but the public should remain cautious as blooms can remain active in cooler months.

Fall and winter recreationists participating in activities such as ice fishing and hunting, can be exposed to cyanoHABs if they are directly exposed to water and should keep animals away from suspicious water and algal mats on the shoreline at known cyanoHAB water bodies. Seek veterinary care immediately if your pets or livestock seem sick after going in or drinking the water.

Cyanobacteria are a natural part of Idaho’s water bodies. When blooms occur, toxic chemical compounds called cyanotoxins can be released into the water. Blooms can have a foul odor and may look like mats, foam, spilled paint, or surface scum. Mats can also form out of sight, on the bottom of the water body.

Staying informed and practicing good water safety habits year-round protects both human and animal health, even outside the peak bloom season.

For more information about cyanoHABs, visit:

• DEQ’s website at www.deq.idaho.gov/water-quality/surface-water/cyanobacteria-harmful-algal-blooms
• DHW’s website at healthandwelfare.idaho.gov/health-wellness/environmental-health/idaho-recreational-waters The Idaho Department of Health and Welfare is dedicated to strengthening the health, safety, and independence of Idahoans. Learn more at healthandwelfare.idaho.gov .