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”. 

 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, including microcystin.  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.

On July 26, 2023, a Harmful Algal Bloom was identified and microcystin was detected at the boat launch area at Hyalite Reservoir in the Custer Gallatin National Forest, and Elk Grove Park Pond.