Montana Issues Kill Order for Invasive Brown Trout in Flathead River

KALISPELL — Montana Fish, Wildlife & Parks has confirmed the detection of a non-native brown trout in the Flathead River upstream of Pressentine Fishing Access Site near Evergreen, raising concerns about potential impacts on native trout populations.

The agency is deploying environmental DNA (eDNA) sampling technology to assess the extent of brown trout presence in the Flathead River and its tributaries, officials announced Monday.

“Protecting our native trout populations is a priority,” said FWP Regional Fisheries Manager Mike Hensler. “Brown trout pose a threat to native species in the Flathead drainage, and we need the public’s help to manage this invasive species.”

Brown trout threaten native species such as bull trout and westslope cutthroat trout by outcompeting them for resources and preying on juvenile fish. The invasive species can disrupt aquatic ecosystems by altering food webs, reducing biodiversity, and threatening native species critical to Montana’s fisheries.

Public Response Requested

FWP is urging anglers who catch brown trout in the Flathead River or its tributaries to kill the fish immediately and report the catch to the FWP Region 1 office at 406-752-5501. Anglers should provide the fish along with the location and date of the catch to assist monitoring efforts.

The environmental DNA sampling method will help identify areas where brown trout may be present, guiding future management actions. This technology can detect genetic material from fish in water samples, allowing biologists to determine species presence without capturing the fish.

Ecological Impact

The illegal introduction of non-native fish and other invasive species can have devastating ecological, recreational and economic impacts on Montana’s waterways. Moving live fish from one waterbody to another is illegal under state law.

Brown trout are identified by their golden brown to yellow-brown color, with dark spots often surrounded by lighter halos, and sometimes with red or orange spots. The species is distinguishable from native trout through these coloration patterns.

The detection represents a significant concern for fisheries managers, as the Flathead River system supports important populations of native bull trout and westslope cutthroat trout. Both species are considered species of concern in Montana due to declining populations and habitat pressures.

FWP officials emphasize that early detection and rapid response are crucial for preventing the establishment of invasive species populations. The agency’s monitoring efforts will continue as biologists work to determine the scope of the brown trout presence in the drainage.

“These species disrupt aquatic ecosystems by altering food webs, reducing biodiversity, and threatening native species critical to Montana’s fisheries,” officials said in the announcement.