Protecting Public Health and the Environment.

Cyanobacteria Harmful Algal Blooms

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 algae and plants. The photosynthetic structures within the bacterial cell contain the blue-green pigments that gave cyanobacteria their former name of “blue-green algae.” Cyanobacteria are present in a water body but typically exist in numbers too small to cause problems (sight, smell, and cyanotoxins). However, a variety of environmental conditions influence cyanobacteria population growth. The right summer time conditions can allow cyanobacteria populations to “bloom” to high enough numbers that a variety of toxins, known as cyanotoxins, are produced. These ideal conditions include warm temperatures, low or slow water flow, high nutrient levels, strong light, and calm weather.

Cyanobacteria harmful algal blooms (HABs) in Idaho can vary in appearance, often looking like pollen, grass clippings, spilled paint, mats, foam, or a 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 can present a real threat to people and animals. Cyanotoxins are thought to primarily be metabolites and used for taking in nutrients. Toxin exposure primarily occurs from ingesting the cyanobacteria and the water they live in but may also occur with skin contact. Ingesting cyanotoxins, which can remain after a visible HAB subsides, can result in a range of health effects from skin irritation and stomach upset to neurotoxic effects and, at very high levels, death. Symptoms in humans are rare; anyone with symptoms should seek medical attention.

If you observe a HAB, contact your DEQ regional office. If in doubt, stay out!


Health Advisories

Current Health Advisories and Map

Health advisories are typically issued by the public health districts, who work closely with DEQ staff.

Take the following precautions when an advisory is in effect:

  • 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.

 Blue-Green Algae at Henrys Lake

Staff Contacts

Water Quality Standards Analyst
Brian Reese
DEQ State Office
Water Quality Division
1410 N. Hilton
Boise, ID 83706
(208) 373-0502

Surface Water Quality Manager
Lance Holloway
DEQ Boise Regional Office
1445 N. Orchard St.
Boise, ID 83706
(208) 373-0550

Surface Water Quality Manager
Bob Steed
DEQ Coeur d'Alene Regional Office
2110 Ironwood Parkway
Coeur d'Alene, ID 83814

Surface Water Quality Manager
Troy Saffle
DEQ Idaho Falls Regional Office
900 N. Skyline Drive, Suite B
Idaho Falls, ID 83402
(208) 528-2650

Surface Water Quality Manager
Sujata Connell
DEQ Lewiston Regional Office
1118 "F" St.
Lewiston, ID 83501
(208) 799-4370

Surface Water Quality Manager
Lynn Van Every
DEQ Pocatello Regional Office
444 Hospital Way #300
Pocatello, ID 83201
(208) 236-6160

Surface Water Quality Manager
Sean Woodhead
DEQ Twin Falls Regional Office
650 Addison Avenue West, Suite 110
Twin Falls, ID 83301
(208) 736-2190

DEQ Resources

Idaho Harmful Algal Bloom Response Plan

Harmful Algal Blooms

Harmful Algal Bloom FAQs

More Information

Harmful Algal Blooms (EPA webpage)

Harmful Algal Blooms (IDHW webpage)

Related Pages

Cyanotoxins: Information for Public Water Systems