Panhandle Health officials are urging people to be cautious when swimming, or fishing in the northern portion of Hayden Lake due to a harmful algal bloom.
Algal blooms can produce dangerous bacteria in high concentrations. They can look like an algal mat or murky, or scummy water.
Health officials are asking people who use Hayden Lake for drinking water to be careful, because boiling, or filtering it may not remove the toxins.
They are also urging people who are exposed algae to wash with clean water.
Algae can also cause harmful toxins to build up in fish caught from the lake, and health professionals are advising people to remove all fat, skin and organs before cooking any fish caught there.
Symptoms of exposure to toxic algae include rash, hives, diarrhea, vomiting, coughing and wheezing. Ingesting water with toxins can also affect the nervous system and liver.