NorthWestern : Harmful algae blooms confirmed on Hebgen Reservoir- advisory issued

Butte, Mont. - July 27, 2021 - Harmful algae blooms (HAB) are present on Hebgen Reservoir in the northeast portion, in the Grayling Arm area, of the reservoir. Routine monitoring of Hebgen has confirmed the presence of toxins, anatoxin-a and microcystin, that pose 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. 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. Animals and livestock that drink large amounts of contaminated water, and pets that collect scum on their fur and then ingest it by licking, are at high risk of 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 people not swim or take part in activities likely to result in exposure to the toxin in areas where the algal bloom is present. Additionally, pets and livestock should be prevented from entering the water in that area.

Harmful algae blooms (HAB) are present on Hebgen Reservoir in the northeast portion, in the Grayling Arm area, of the reservoir.

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 algal 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.

Blue-green algal 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.

Advisory signs are at public access points in the Grayling Arm area warning the public that toxic algae has been identified in the water in these areas. At this time there are no other identified blooms affecting other areas of the reservoir.

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

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

Report a suspected HAB at www.hab.mt.gov 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.

Follow NWE on Facebook or on Twitter (@NWEinfo) and the Gallatin City-County Health Department (@GallatinHealth)

About NorthWestern Energy (Nasdaq: NWE)

NorthWestern provides electricity and / or natural gas to approximately 743,000 customers in Montana, South Dakota, and Nebraska. We have generated and distributed electricity in South Dakota and distributed natural gas in South Dakota and Nebraska since 1923 and have generated and distributed electricity and distributed natural gas in Montana since 2002. More information on NorthWestern is available on the company's website at www.northwesternenergy.com.

Media Contacts:

NorthWestern Energy
Jo Dee Black
866-622-8081
[e-mail]

Montana Department of Environmental Quality, Watershed Protection Section
Hannah Riedl
406-444-0549
[e-mail]

Gallatin City-County Health Department
Lori Christenson
406-582-3100
[e-mail]