Threat to Native Species Prompts State Investigation
Montana Fish, Wildlife and Parks has confirmed the presence of invasive brown trout in Ashley Lake and Church Slough after multiple anglers reported catches in recent months. The discovery marks a significant concern for fisheries managers protecting native fish populations in waters connected to the Flathead River drainage.
The first brown trout surfaced in February when an angler photographed and released the fish after catching it in Ashley Lake, initially uncertain about the species identification. A second specimen was subsequently caught in Ashley Lake and delivered to state biologists for analysis, while a third brown trout was documented through photographs taken by an angler in Church Slough and reported to Montana wildlife officials.
Kenny Briedinger, a fisheries biologist with Montana Fish, Wildlife and Parks, emphasized the severity of the situation. “This is a big deal. We take this one very seriously. There is a lot of potential for harm from brown trout in the drainage,” he said.
How Brown Trout Threaten the Ecosystem
Brown trout are classified as an invasive species in the region and present a dual threat to the native fish community. The predatory fish actively hunt smaller native species while simultaneously competing for food and habitat resources, potentially destabilizing the ecosystem that native populations depend upon for survival.
Ashley Lake and Church Slough maintain hydrological connections to the Flathead River system, meaning any established brown trout population could spread to adjacent waters and expand the threat across a broader area.
State officials suspect the brown trout were illegally introduced to Ashley Lake. The lake’s only outlet, Ashley Creek, is blocked by a dam, which would have prevented natural colonization by brown trout from downstream sources. This structural isolation suggests deliberate human introduction as the most likely explanation for their presence.
Investigation Into Origin and Spread
Investigators have been pursuing potential brown trout sightings across the drainage for several months. A photograph surfaced last summer showing what appeared to be a brown trout upstream of the Pressentine Fishing Access Site in Evergreen, but state officials were unable to verify the sighting due to insufficient landmarks in the image.
DNA testing of water samples collected from the Flathead River itself detected no brown trout genetic material, suggesting the problem may be localized to specific waterways rather than widespread throughout the main stem river system.
State fisheries biologists plan to conduct trace-element analysis of ear bones from the caught brown trout, a technique that can determine where the fish were born and may reveal whether multiple populations exist or if all discoveries trace to a single introduction event.
Public Response and Prevention Measures
Montana Fish, Wildlife and Parks is urging anglers throughout the Flathead River drainage to take direct action if they encounter brown trout. Fisheries managers are asking all anglers who catch brown trout upstream of the SKQ Dam to kill the fish immediately and report the catch to Montana Fish, Wildlife and Parks Region 1.
Identifying brown trout in the field can help anglers respond appropriately. The species typically displays a golden brown or yellow-brown coloration with dark spots surrounded by lighter halos. In larger waterbodies, brown trout may appear more silvery with a dark green back, making identification slightly more challenging in those environments.
Anglers and residents who spot brown trout or have additional information about the discoveries are encouraged to contact Montana Fish, Wildlife and Parks Region 1 at 406-752-5501.
The discovery underscores ongoing challenges facing Idaho and Montana natural resource managers in protecting native fish populations from invasive species introductions. Similar management concerns have shaped broader conservation efforts across the Bonner and Boundary County region, where agencies continue balancing resource protection with recreational and economic uses of public lands and waterways.