Advisory issued to avoid eating fish in section of Clark Fork

The State of Montana Fish Guidance Board, which includes Montana Fish, Wildlife & Parks and the departments of Environmental Quality, and Public Health and Human Services, has updated the fish consumption guidance for all species of fish on a 148-mile stretch of the Clark Fork River and tributaries in western Montana in response to new research results.

Guidance now recommends avoiding consumption of all species of fish from the Clark Fork River’s confluence with the Bitterroot River, just west of Missoula, to the confluence with the Flathead River, near Paradise. Slightly revised guidance is also in place for rainbow trout and northern pike on an upstream section of the Clark Fork and for the Blackfoot and Bitterroot rivers.

New data was collected to assess chemical contaminants including dioxins, furans, and PCBs in fish tissue in a study area on the Clark Fork that extended from approximately 30 miles upstream of Missoula to 100 miles downstream.

Testing in the area is underway as part of water quality monitoring around the former Smurfit-Stone Container mill site. Upon review of the study results, new guidance was issued based on high levels of contaminants in the fish tissue. The source of all the contaminants found in the fish has not been attributed.

The study only looked at contaminant concentrations found in the muscle tissues of northern pike and rainbow trout, but the same “Avoid” guidance extends to all species present in the Clark Fork River near Missoula (such as brown trout, whitefish, small- and large-mouth bass, northern pikeminnow, and sucker species) because similar food habits, habitat use, and life-span suggest they could also contain chemical concentrations at potentially dangerous levels.

At high levels of exposure, the contaminants found in the fish have been linked to adverse human health effects in the immune and nervous systems and may be associated with birth defects.

Dioxins and PCBs are classified as definite and probable human carcinogens, respectively, at high and prolonged levels of exposure. Fish consumption guidelines are denoted as “Avoid” in the table where consumption of fish is not recommended.

Fish consumption guidance is conservative and designed to protect the most sensitive members of the population over a lifetime. In addition, the risks are based on the amount of contaminants found in a raw fillet. Using normal cooking practices, and keeping only smaller fish, can reduce exposure risks.

For more information about the human health effects of eating fish, contact DPHHS at 406-417-9848.

For information about fish advisories on the Clark Fork River and throughout Montana, contact FWP at 406-444-5686, or visit FWP's website at fwp.mt.gov. Click “FishMT," then click "Fish Consumption Guidelines."