Official Government Website

Cyanobacteria Harmful Algal Blooms

This page provides information related to current recreation water quality health advisories involving cyanobacteria harmful algal blooms (HABs) and E. coli bacteria. The map is updated with the most current information as health advisories are issued and lifted throughout the season. For more information about how we respond to cyanobacteria blooms see the questions and answers below and more information in our storymap.

When in Doubt, Stay Out!

Active Harmful Algal Bloom Advisories

County Waterbody Date Issued Dominant Taxa DEQ Contact

Lifted Harmful Algal Bloom Advisories

County Waterbody Date Issued Date Lifted
Kootenai Fernan Lake 47/22/2020 12/23/2020
Ada Silver Lake 4/28/2020 8/21/2020
Washington Brownlee Reservoir 7/10/2020 11/30/2020
Adams Hells Canyon Reservoir 7/10/2020 11/10/2020
Twin Falls Cedar Creek Reservoir 8/11/2020 11/13/2020
Twin Falls Thorn Creek Reservoir 8/11/2020 11/13/2020
Camas Mormon Reservoir 8/21/2020 11/13/2020
Canyon Lake Lowell 9/4/2020 11/23/2020
Bonner Lake Cocolalla 9/4/2020 10/28/2020
Owyhee CJ Strike Reservoir 9/18/2020 10/29/2020
Latah Hordemann Pond 8/11/2020 11/16/2020
Bonner Round Lake 10/2/2020 10/28/2020
Latah Spring Valley Reservoir 10/2/2020 12/7/2020
Valley Cascade Reservoir 10/5/2020 11/25/2020
There are no current E. coli advisories at this time.

This accordion will not appear on the screen

Cyanobacteria are photosynthetic bacteria that occur naturally in Idaho’s lakes and rivers. Many of us learned about “blue-green algae” in school, but these algae are actually bacteria that photosynthesize like plants. The photosynthetic structures within the bacterial cell contain the blue-green pigments that give cyanobacteria their color and their name.

Cyanobacteria are present in nearly all water bodies but typically exist in numbers too small to cause problems (sight, smell, and cyanotoxins). However, a variety of environmental conditions influence cyanobacteria population growth. Summertime conditions can allow cyanobacteria populations to “bloom” to high enough numbers that a variety of toxins, known as cyanotoxins, are produced in quantities that can be harmful to people and animals. These ideal conditions include warm temperatures, low or slow water flow, high nutrient levels, strong light, and calm weather.

Cyanobacteria harmful algal blooms (blooms) in Idaho can vary in appearance, often looking like bright green water or pea soup, pollen, grass clippings, spilled paint, mats, green or blue-green foam, or dense surface scum. Blooms can range in color from blue and bright green to brown, red, and even white. Some blooms may produce a foul odor.

Cyanotoxins present a  real health threat to people and animals. Toxin exposure primarily occurs from ingesting the cyanobacteria and the water they live in but it also occurs with skin contact. Ingesting cyanotoxins, which can remain after a visible bloom subsides, can result in a range of health effects, many of which are easily misdiagnosed. Symptoms include:

  • skin irritation
  • upset stomach
  • Hay fever or allergies
  • neurotoxic effects, which includes trouble breathing
  • at very high levels, death.

Anyone with symptoms should seek medical attention.

  • Avoid exposure to water experiencing a HAB. Take extra precautions to ensure children, pets, and livestock are not exposed to the water.
  • Do not consume water with a HAB. Neither boiling nor disinfecting water removes cyanotoxins from water.
  • Consume only the fillet portion of fish exposed to a HAB. Cyanotoxins can accumulate in fish. Removing the fat, organs, and skin minimizes the exposure. Wash hands after handling. The risk associated with consuming fish caught in waters with a HAB is unknown and under research.
  • Enjoy the other recreation opportunities in the area!

*Health advisories are intended to advise the public about a potential health risk. Health advisories are not water body closures.

This accordion will not appear on the screen

Water Quality Standards Analyst

Brian Reese
(208) 373-0570

ver: 3.4.0 | last updated:
Jump back to top of page button