Three of Montana's Most Polluted Lakes Revealed

Experts warn of toxic contamination and microplastics in popular waterways

Published on Mar. 4, 2026

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Montana's lakes and rivers are facing growing pollution challenges, with three of the state's most polluted lakes identified as the Berkeley Pit in Butte, Flathead Lake, and Lake Koocanusa. Experts warn that toxic contamination, microplastics, and other pollutants threaten the state's natural beauty and thriving tourism industry.

Why it matters

Protecting Montana's pristine lakes and rivers is crucial for the state's environment, wildlife, and lucrative tourism industry. Pollution in these waterways can have devastating impacts, killing birds and other wildlife, and making the water unsafe for human use and enjoyment.

The details

The Berkeley Pit in Butte is designated as a Superfund site, with water so toxic that birds are prohibited from landing on it. Flathead Lake, one of Montana's most picturesque lakes, has been found to contain microplastics. Lake Koocanusa, which stretches 90 miles near the northern border, has dealt with selenium and other pollutants tied to coal mining.

  • The Berkeley Pit has been monitored and treated by the Environmental Protection Agency since 1983.
  • Researchers at the University of Montana recently found microplastics in the water of Flathead Lake.
  • Pollution issues in Lake Koocanusa have been ongoing, according to the Montana Environmental Information Center.

The players

Berkeley Pit

A designated Superfund site in Butte, Montana, with water so toxic that it can kill birds within hours if they land on it.

Flathead Lake

One of Montana's most picturesque lakes, which has been found to contain microplastics according to researchers at the University of Montana.

Lake Koocanusa

A 90-mile long lake near the northern border of Montana that has dealt with selenium and other pollutants tied to coal mining, according to the Montana Environmental Information Center.

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The takeaway

The pollution issues facing Montana's lakes highlight the need for continued vigilance and environmental protection efforts to preserve the state's natural beauty and thriving tourism industry. Addressing sources of contamination, such as mining and microplastics, will be crucial to ensuring these waterways remain clean and safe for wildlife and human enjoyment.