Public Health Advisory: Harmful algal bloom identified in Island Park Reservoir

DHW Communications

The Idaho Department of Health and Welfare (DHW) is issuing a health advisory for Island Park Reservoir, urging caution when recreating in or near the water.

Recent samples from Island Park Reservoir showed high amounts of toxin-producing cyanobacteria. The toxins they produce (cyanotoxins) can be harmful to people, pets, and livestock.

DHW works closely with the Idaho Department of Environmental Quality (IDEQ) to identify, respond to, and monitor cyanobacteria harmful algal blooms (cyanoHABs). Please visit the Idaho Recreational Water Health Advisories tab at the Get Healthy Idaho website for advisories and sampled locations at water bodies throughout Idaho.

When recreating near or in Island Park Reservoir, take the following precautions while the advisory is in effect:

  • Avoid swimming, wading, or other contact with the water. Take extra care to ensure children do not drink or get water on them.
  • Ensure pets and livestock do not drink or go into the water. If they have contact with the water, clean skin, hide, or fur with clean water right away.
  • Do not drink or cook with the water. Boiling or filtering the water does not remove the toxins and can increase the risk of becoming sick.
  • Wash hands thoroughly in clean water after handling fish or objects from the water.
  • If you choose to eat fish from the water, clean and wash fish thoroughly in uncontaminated water. Filet the fish, and remove all fat, skin, and internal organs before cooking. Cyanotoxins can build up in fish, and the risk to people is unknown.
  • Watch for symptoms. If you touch or swim in the water or inhale water droplets, you might experience a rash, hives, red eyes, wheezing, coughing, or shortness of breath. If you swallow the water, you might have stomach pain, diarrhea, or vomiting. You might have a headache, muscle weakness, or dizziness. If your liver is damaged, your skin might turn yellow, and you will have dark urine. If you think you might be sick from cyanotoxin, consult your healthcare provider or call the poison center at 1-800-222-1222. In addition, notify
  • Monitor media reports and DHW’s website for health advisories.

Cyanobacteria are a natural part of Idaho’s water bodies. The amount of bacteria usually increases rapidly when the temperature of the water rises and there are nutrients for the bacteria to grow (bloom). The blooming can release toxic chemical compounds (cyanotoxins) into the water.

Blooms don’t all look the same. They may look like mats, foam, spilled paint, or surface scum, and have a foul odor. Algal mats can be out of sight on the bottom of the water body.

Pets, livestock, and wildlife can get sick or die within minutes to days after cyanotoxin exposure. Dogs can become sick first because they are more likely to swim in or drink contaminated water or lick contaminated water or bloom material from 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 more information about cyanoHABs:

The public will be advised when it is likely the concern no longer exists.

The Idaho Department of Health and Welfare is dedicated to strengthening the health, safety, and independence of Idahoans. Learn more at