Toxic Algae in Idaho

Who tracks blooms in Idaho

Two state agencies share the work. The Idaho Department of Environmental Quality (DEQ) responds to bloom reports, samples lakes and reservoirs and reviews the results. It passes that information to the Idaho Department of Health and Welfare (DHW) and the local public health district, and DHW decides whether a public health notice is needed.

DEQ cannot watch every lake all the time, and blooms can build quickly in hot weather. Many lakes in Idaho are never sampled, so no warning does not mean no bloom.

What the three warning levels mean

DEQ tests for cyanobacteria cell counts and, when possible, for the toxins themselves. It follows EPA recommended thresholds for microcystins and cylindrospermopsin and uses a cell count threshold for Microcystis.

Check before you go

• DHW recreational water health advisories map shows current advisories by water body.
• DEQ harmful algal blooms page has the current risk table and a sign up for bloom email updates.
• Look at the water yourself. Blooms can look like spilled paint, pea soup, surface scum or grass clippings, and they often pile up along the shore downwind. See what a bloom looks like.

How to report a bloom in Idaho

• Call DEQ at (866) 671-5385.
• Email algae@deq.idaho.gov.
• Use the online report form on the DEQ harmful algal blooms page.

A photo of the bloom and the exact location help DEQ decide whether to sample. For local questions, DEQ suggests calling your DEQ regional office.

Keeping people, pets and livestock safe

• People: stay out of water with a bloom. If you do have contact, rinse off right away with soap and clean water, and see a doctor if you feel sick. In an emergency, call 911.
• Dogs: keep them out of the water. Dogs drink the water and lick scum off their fur, so they are often the first to get sick. Rinse them with clean water and call a vet if they seem ill.
• Livestock: keep animals from drinking at a bloom. Pets and livestock can become sick or die within minutes to days.
• Fish: health officials advise washing your hands after handling fish from a bloom, cleaning fish in clean water and removing the internal organs before eating.

DEQ’s short version: when in doubt, stay out.

Drinking water

Never drink untreated lake water during a bloom. Boiling does not remove cyanotoxins and can concentrate them, and most backpacking filters do not work on them. DEQ notes that home units certified to NSF Protocol 477 can reduce microcystins.

Public water systems in Idaho are not required to test for cyanotoxins, although some do so on their own.

EPA swimming advisory values

The US Environmental Protection Agency recommends a swimming advisory whenever microcystins are above 8 micrograms per liter or cylindrospermopsin is above 15 micrograms per liter on any single day. Idaho DEQ follows EPA recommended thresholds when it weighs a Health Advisory.

You cannot tell whether a bloom is making toxins by looking at it, and toxin levels can change from one week to the next. Only a lab test can tell you what is in the water.

Private and community lakes

State sampling focuses on public water. If you manage an HOA lake, a golf course lake or a private lake, nobody else is likely to test it. Our algae ID and cyanotoxin analysis tells you which algae are present and whether toxins are in the water, and a nutrient plan goes after what feeds the bloom in the first place.

Sources, checked November 4, 2026. Idaho DEQ, Cyanobacteria Harmful Algal Blooms. Idaho DHW, Recreational Water Health Advisories. Central District Health, Harmful algae bloom season. US EPA, Protecting Human Health from Cyanotoxin Exposure During Recreation. US EPA, Recreational criteria and swimming advisories for microcystins and cylindrospermopsin (2019).