Scientists with the University of Montana found per- and polyfluoroalkyl substances — commonly known as PFAS or "forever chemicals" — in water samples from every location they tested last fall across the state's Flathead Watershed.
The findings, along with a separate study showing pharmaceuticals and personal care products in nearby waters, suggest persistent contaminants are turning up even in places known for their natural beauty.
What's happening?
Water collected in fall 2025 from Flathead Lake, the Flathead and Swan rivers, and Stoner Creek all contained PFAS, according to sampling conducted by the University of Montana's Flathead Lake Biological Station.
The university's announcement said researchers looked for 40 PFAS compounds and identified 10. Three of those were present at levels exceeding the laboratory reporting threshold, while levels of the compounds with defined safe drinking water standards remained far below those thresholds.
"Detection of these compounds is not entirely surprising given results elsewhere," Jim Elser, director of the Flathead Lake Biological Station, said in the announcement. "But confirming their presence in the Flathead, even at these low levels, is still a matter of concern."
A second study by the station found pharmaceuticals and personal care products at each location sampled in Ashley Creek, Flathead Lake, and Whitefish Lake.
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The station said the detections ranged from caffeine and medications — both prescription and over-the-counter — to lotions, soaps, sunscreen, and controlled substances. Such chemicals can indicate wastewater, human waste, or improperly disposed products.
Why does this matter?
The nickname "forever chemicals" refers to the substances' persistence in habitats and human bodies. The lasting chemicals are found in many everyday and industrial products, including clothing, carpets, food packaging, wire coatings, pesticides, and herbicides.
Even though the concentrations measured in the Flathead Watershed were low, safe drinking water benchmarks have not been set for many PFAS compounds. Researchers are also still trying to pin down what long-term exposure could mean for ecosystems and for individuals.
Meanwhile, exposure to certain levels of PFAS has been associated with a range of human health concerns, including reproductive issues, developmental problems, cancer risks, and immune impairment.
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Finding pharmaceuticals and personal care products, meanwhile, may point researchers toward sewage or septic trouble spots in communities that depend on clean water for drinking, fishing, tourism, and outdoor recreation.
What's being done?
For now, scientists at the Flathead Lake Biological Station say the priority is to expand both monitoring and research.
Elser said one major obstacle is the price of testing, since analyzing water for PFAS can be costly.
Using medication take-back programs instead of flushing drugs, maintaining septic systems, and taking care when disposing of household chemicals can help reduce some contamination pathways.
"Right now, PFAS concentrations are not at levels to cause direct concern about human health, but they should motivate us to find out more about where they are coming from and to continue surveillance," Elser said.
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