Harmful Algal Blooms

blue green algae

Harmful Algal Blooms (HABs) & Blue Green Algae

Excerpts of information from Idaho Department of Environmental Quality & Idaho Dept of Health and Welfare

Impacts & Advisories for Ada, Elmore, Boise and Valley Counties

No current advisories to report in Public Health District 4.
  • For a map of statewide harmful algal blooms and related health advisories, click HERE. (link to the DEQ's website)

Past (Lifted)

Most of the year Idaho's beautiful lakes, reservoirs and ponds are safe to enjoy. However, when water temperatures rise and the right type of nutrients are available, some bodies of water can produce harmful algal blooms (HABs). These can pose health risks to humans, pets, livestock, and wildlife. 

What is a Harmful Algal Bloom?

Harmful algal blooms are actually bacteria (not algae) that can produce toxins. When weather conditions are calm and there is an increase in water temperature and nutrients, they can rapidly increase in number, producing a bloom. Blooms can vary in appearance, sometimes looking like mats, foam, or surface scum — especially near the shoreline. Blooms can range in color from blue and bright green to brown and red. Some blooms produce a foul odor.

Blooms can occur at any time, but they most often occur in late summer or early fall. Often in association with a HAB, you may hear reference to blue-green algae, which are a type of cyanobacteria.

Impacts to Health

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 or pain to neurotoxic effects and at very high levels, death.

The most common health effects are skin and eye irritation. Other more severe health effects can include:

> Difficulty breathing
> Stomach pain
> Nausea
> Vomiting
> Diarrhea
> Dizziness
> Numbness and tingling in lips, fingers, and toes

Symptoms can occur within an hour of exposure but may take as long as 36 hours to develop depending on the particular toxin and its concentration (CDC 2016). Anyone with symptoms should seek medical attention.

Protect Yourself and Pets

People and animals can be exposed to HABs by swallowing water and/or touching the water during recreational activities such as swimming, water skiing, and diving.

While Central District Health works closely with the Idaho Department of Environmental Quality (DEQ) and other agencies when HABs are identified, the best advice is, when in doubt, stay out.

and recommends 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.

Symptoms can occur within an hour of exposure but may take as long as 36 hours to develop depending on the particular toxin and its concentration (CDC 2016). Anyone with symptoms should seek medical attention. If you experience mild irritation, rinse with clean water immediately.

If your pet comes in contact with a bloom, rinse them with clean, fresh water immediately. If severe symptoms occur, call a veterinarian. In severe cases, animals may die within tens of minutes to hours after they have been exposed to harmful algal blooms. When harmful algal blooms decompose, they can also kill fish that live in the water.  

How to Report Potential HABs

You can help report potentially harmful algal blooms in Idaho:
Idaho DEQ - Bloomwatch Reporting Site


Idaho DEQ: Blue-Green Algae and Harmful Algal Blooms
Idaho Health & Welfare: FAQs About Harmful Algal Blooms

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