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Toxic algae blooms confirmed on Hebgen Reservoir

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BUTTE – Toxic algae blooms are present on Hebgen Reservoir near the Corey Spring area of the Grayling Arm of the reservoir and Rainbow Point Campground and Boat Launch. Routine monitoring of Hebgen has confirmed the presence of a toxin, anatoxin-a, that poses a risk to people, pets and livestock.

Ingestion or prolonged contact with the algal bloom may result in illness, with signs such as muscle twitching, staggering, convulsions, paralysis and death. Livestock that drink large amounts of contaminated water and pets that collect scum on their fur then ingest it by licking are at highest risk from toxin exposure. Toxin exposure can occur in humans from recreational activities where water might be ingested such as swimming, wind surfing, jet skiing, and water skiing.

Health experts recommend that people not swim or take part in activities likely to result in exposure to the toxin in areas where the algal bloom is present and that pets and livestock be kept away from entering the water in that area.

Importantly, “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,” said Hannah Riedl, water quality specialist at the Montana Department of Environmental Quality.

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 cyanotoxins. 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 like roots, mosses, or water plants. Warning signs are at public access points at both the Corey Spring and Rainbow Point warning the public that toxic algae has been identified in the water in these areas. At this time there are no other identified blooms affective other areas of the reservoir.

NorthWestern Energy is monitoring the blooms and will provide updates if additional restrictions are implemented for public safety.

Report a suspected HAB at or call 1-888-849-2938. You may also report a suspected HAB by calling the Gallatin City-County Health Department Environmental Health at 406-582-3120.

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