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. 

Recreation Water Bloom Advisories and Warnings

Active Advisories

County Waterbody Date Issued Dominant Taxa DEQ Contact

Lifted Advisories

County Waterbody Date Issued Date Lifted
  • Report a Potential Bloom
  • Health Effects
  • FAQs

Report a Health Concern

Idaho’s health agencies are responsible for educating and advising the public on cyanobacteria exposures.

Idaho’s seven public health districts develop public health advisories, in consultation with DEQ, based on lab result analysis. The Idaho Department of Health and Welfare maintains a Harmful Algal Blooms FAQ page and Waterborne Illness page, which contain educational material and general information about potential illnesses from recreational waters and drinking.

For information on health concerns and cyanobacteria, please contact the Idaho Department of Health and Welfare or your local public health district.

Report a Potential Cyanobacteria Harmful Algal Bloom

Use the link below to provide information about a potential cyanobacteria harmful algal bloom.

  • 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.

For more information on health-related questions, please contact the Idaho Department of Health and Welfare or your local public health district:

What Are Cyanobacteria?

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.

Where And When Do Cyanobacteria Blooms Occur?

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.

What Do They Look Like?

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.

What Should I Do If A Health Advisory Is Issued?

  • 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.

Can a Bloom Affect My Drinking Water?

Cyanobacteria and cyanotoxins can present dangers if you receive your drinking water from surface water (or influenced by surface water). However, the toxins can be removed safely before reaching the distribution system through specific treatment methods. Learn about drinking water and cyanobacterial harmful algal blooms on our Contaminants in Drinking Water web page.

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Water Quality Standards Analyst

Brian Reese
(208) 373-0570

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