Gem State Roundup

South Central Idaho health officials warn of unhealthy toxin levels in Cedar Creek Reservoir

By: - August 29, 2023 3:00 pm
cyanobacterial bloom in water

If the water in Idaho’s rivers and lakes smells bad, looks foamy or thick (like paint was spilled into the water), appears scummy, blue-green, or brownish-red in color, stay out, health officials advise. (Courtesy of the Centers for Disease Control and Prevention)

Idaho’s South Central Public Health District has issued a public health advisory for Cedar Creek Reservoir, also known as Roseworth Reservoir, due to toxins being found in the water from a harmful algal bloom, according to a press release.

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

The Idaho Department of Environmental Quality’s testing shows levels of a cyanotoxin, Microcystin, are now at unhealthy levels in the reservoir. Increased levels of this toxin are caused by cyanobacteria, and exposure can be harmful to people, pets and livestock.

When recreating at Cedar Creek Reservoir the public is advised to take the following steps to protect their health, according to the health district:

  • Avoid exposure to water in reservoirs under this kind of health advisory. Make sure children, pets and livestock are not exposed to the water.
  • Do not drink water from the reservoir. Boiling and disinfecting do not remove toxins from the water.
  • Do not allow pets to eat dried algae.
  • If you choose to eat fish from the water, remove all fat, skin and organs before cooking. Toxins are more likely to collect in those tissues. Wash hands after handling.

“This is the second advisory we’ve issued in our region,” said Josh Jensen, environmental health director for the district, in the press release. “Toxins from (harmful algal blooms) can be harmful to humans as well as pets, so we urge you to check any reservoir you want to recreate in before you, or your pets, enter the water.”

The second advisory was issued in July for Salmon Falls Creek Reservoir, which remains in effect. Similar advisories are also still in place at the Hells Canyon Reservoir and Brownlee Reservoir. To see a map of all health advisories around the state, check out this map online.

Harmful algal blooms are not unusual in warm summer months and typically shrink quickly as the water temperature drops in mid-to-late fall. The health district will issue another press release when DEQ tests show toxin levels in this reservoir are at safe levels again, the release said.

More information is available at:


Our stories may be republished online or in print under Creative Commons license CC BY-NC-ND 4.0. We ask that you edit only for style or to shorten, provide proper attribution and link to our web site.

Christina Lords
Christina Lords

Christina Lords is the editor-in-chief of the Idaho Capital Sun and has been a professional journalist covering local and state government since graduating from the University of Idaho in 2009. A Pocatello native, Lords is a fifth-generation Idahoan who served as a reporter at the Moscow-Pullman Daily News and the Post Register in Idaho Falls and served as assistant editor for the Idaho Press in Nampa. She also led the Idaho Statesman in Boise for two years before turning to nonprofit journalism.