The U.S. Environmental Protection Agency (EPA) will conduct a sampling project in the Clark Fork, Bitterroot and Blackfoot rivers in Montana to better understand the distribution of polychlorinated biphenyls (PCBs) across the watershed.

EPA Region 8 scientists will analyze sediment and aquatic insects as part of the project, expanding on previous federal and state sampling that has primarily focused on fish tissue and potential human exposure through fish consumption. The sampling area will extend 100 miles upstream of the confluence of the Clark Fork and Flathead rivers to provide a broader assessment of PCB levels across the three watersheds.

The persistent chemicals were widely used in industrial applications before production was banned in 1979 and can accumulate in organisms and move through the food chain. Montana Department of Fish, Wildlife and Parks and the Confederated Salish and Kootenai Tribes have issued PCB-related fish consumption advisories for the waterways included in the project.

Sampling is expected to take place from late August through early September 2026, with results anticipated in summer 2027. EPA said the effort is intended to address data gaps and provide tribes, state agencies, community groups and other stakeholders with a clearer picture of current PCB contamination.