Serving Ada, Boise, Elmore, and Valley Counties



Harmful Algae Bloom Season is Here

Beware of harmful algal blooms when recreating in bodies of water

BOISE, July 27, 2023 – The Southwest and Central Health Districts want to inform the public of the risk of illness in the region when recreating in bodies of water that have Harmful Algal Blooms (HABs) during the summer months.

During the HAB season, naturally occurring cyanobacteria will become more active with warmer temperatures. When there are more nutrients in the water for the bacteria to feed on, the bacteria can create large algae blooms, some of which produce toxic chemical compounds, or cyano-toxins, which can be fatal to animals and humans. Blooms can vary in appearance, and may look like mats, foam, spilled paint, or surface scum, and have a foul odor.

While the Idaho Department of Environmental Quality (DEQ) tests some bodies of water in Southwest and Central Idaho regularly, many bodies of water throughout the state are not monitored for HABs, so recreators should watch for the signs of HABs to avoid exposure.

When toxin levels are greater than the health standard, the Idaho Department of Health and Welfare will issue advisories for those specific bodies of water and post updated information on their interactive online map. Both health districts urge residents and recreators to find information on the body of water they plan to interact with to make an informed decision before they recreate.

When recreating near or in a body of water impacted with cyano-toxins, take the following precautions:

  • Avoid swimming, wading, or other activities in the water. Take extra precautions to ensure children, pets, and livestock are not exposed to the water. Do not drink or cook with water containing a bloom. Boiling and filtering the water does not remove the toxins and can increase the risk of adverse health effects.
  • Wash hands thoroughly in clean water after handling fish caught in water experiencing a bloom. Cyanotoxins can accumulate in fish and the risk to people is being researched. Clean and wash fish thoroughly in uncontaminated water and dispose of internal organs before consumption.
    If you choose to eat fish from this area, filet the fish and remove all fat, skin, and organs before cooking.
  • Clean skin or pet fur with clean water as soon as possible after any water contact.

Symptoms of cyanotoxin exposure include rashes, hives, diarrhea, vomiting, coughing, and/or wheezing. More severe symptoms affecting the liver and nervous system may result from ingesting water. If symptoms persist, consult your healthcare provider.

Pets, livestock, and wildlife can get sick, or even die, within minutes to days after cyanotoxin exposure. Dogs are often the first affected because they are more likely to swim in or drink contaminated water or lick contaminated water or bloom material off their fur. If your pets or livestock have been in the water, immediately wash them with clean water to keep them from licking cyanobacteria off their bodies. Seek veterinary care immediately if your pets or livestock seem sick after going in or drinking the water.

For current information about harmful algal blooms, and advisories, visit DHW’s site and interactive map or DEQ’s website.



DEQ media contact:
DHW media contact:
SWDH media contact:
CDH media contact:

Anna Marron
Greg Stahl
Monique Evancic
Maria Ortega


About Central District Health
CDH, Public Health District IV, is one of seven public health districts within the state of Idaho, serving the counties of Ada, Boise, Elmore, and Valley. With a vision of Healthy People in Healthy Communities, CDH’s emphasis is on decreasing risk factors for chronic disease, improving quality of life and increasing the years of healthy life among residents.

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