Protecting Public Health and the Environment.

Blue-Green Algae and Harmful Algal Blooms

Blue-green algae are not algae at all but are photosynthetic bacteria, also known as cyanobacteria. There are several species of blue-green algae, which thrive under their own unique conditions and produce a variety of toxins. Blue-green algae are naturally occurring and usually present in a water body, but they typically exist in numbers too small to cause problems. Blue-green algae growth is influenced by a variety of environmental conditions including temperature, flow, nutrient levels, light, weather, vertical mixing in the water column, and pH levels.

Given the right conditions, high concentrations of blue-green algae can occur and form a bloom. Blooms can vary in appearance, sometimes looking like mats, foam, or surface scum. Blooms can range in color from blue and bright green to brown and red. Some blooms produce a foul odor. Not all blooms are toxic, but when toxic harmful algal blooms do occur they present a health risk to humans, pets, and livestock. Exposure may occur from ingestion, skin contact, or inhalation. Exposure 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 blue-green algae bloom, contact your DEQ regional office.

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 harmful algal bloom. Take extra precautions to ensure children, pets, and livestock are not exposed to the water.
  • Do not consume water with a blue-green algae bloom. Neither boiling nor disinfecting removes blue-green algae toxins from water.
  • If fish are known to have been exposed to a blue-green algae bloom, only consume the fillet portion (remove the fat, organs, and skin). Wash hands after handling. The risk associated with consuming fish caught in waters with a blue-green algae bloom is unknown. Toxins produced by blue-green algae can accumulate in the organs of fish.

 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) 373-0570

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

Water Quality Manager
Thomas Herron
DEQ Coeur d'Alene Regional Office
2110 Ironwood Parkway
Coeur d'Alene, ID 83814
(208) 666-4631

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

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

Water Quality Manager
Kiley Mulholland
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

Blue-Green Algae and Harmful Algal Blooms: Information for Public Water Systems