Contact MT DPHHS with a possible HAB:

Contact the Gallatin City-County Health Department with a possible HAB:

As Montanans and visitors head to local ponds, lakes and reservoirs for late summer fun, public health official urge citizens to know the health risks of Harmful Algal Blooms, or “HABs”.

Below is more information for HABs in Gallatin County!

HABs are caused by blue-green algae that are native to Montana’s freshwater lakes and reservoirs.  Not all varieties of blue-green algae are harmful, but some can produce dangerous cyanotoxin.  Blue-green algae blooms often look like pea soup, grass clippings, or green latex paint.  The algae are usually suspended in the water or appear as floating mats; they do not grow from the bottom with roots like other water plants.


Image credit: Examples of Harmful Algal Blooms (HABs) – Utah Department of Environmental Quality

In past summers, algal blooms have been identified in a number of Gallatin County surface waters including Hyalite Reservoir, Mystic Lake, Hebgen Lake and numerous smaller subdivision ponds.

Ongoing drought conditions and high temperatures could increase algal bloom activity in the county.

We encourage all recreationists to exercise caution and to avoid algal blooms that could potentially produce toxins that pose a risk to people, pets, and livestock.

Children and pets are more likely to ingest HAB infested waters because they spend most of their time wading in the shallow waters where algae can accumulate, and they have less control over how much water they ingest.

When in doubt, stay out!

Do not drink, swallow, or swim in water that shows signs of a HAB and be sure to keep kids, pets, and livestock away as well.

Because tracking rapidly changing conditions in every body of water is not feasible, we want to inform everyone enough to make their own recreational decisions. We also ask you to help by reporting HABs so that we can respond quickly and hopefully prevent people, pets, and livestock from getting sick.

Report a suspected HAB at or call 888-849-2938.  You may also report a suspected HAB by calling the Gallatin City-County Health Department Environmental Health Services at 406-582-3120.

HAB Fact Sheet

Direct contact, ingestion or inhalation of cyanotoxins may irritate the skin, eyes, nose and respiratory system or cause nausea, vomiting, diarrhea or headaches.

If you suspect a HAB-related illness in a person or animal, call Poison Control 1-800-222-1222 and seek medical attention.

When a HAB is reported to either DEQ or directly to the Gallatin City-County Health Department, it is investigated to determine whether the bloom is nuisance green algae or potentially toxic blue-green algae.  In Gallatin County, the health department then works with the entities managing the waterbody to determine whether water quality test results warrant safety advisories.

For more information and details on HABs in Montana, visit the MT DPHHS website.