Montana Fish, Wildlife and Parks has confirmed non-native brown trout at two locations in the Flathead drainage, and its instruction to anglers is blunt: kill any brown trout caught above SKQ Dam, then report it.
The first confirmation came from photographs an angler took at Ashley Lake in February. As the Daily Inter Lake reported, the fisherman was unsure what he had reeled in, photographed the fish and released it. A second brown trout was later caught in the same lake and handed to state biologists. A third, from Church Slough on the Flathead River, was reported by photograph in late July.
"This is a big deal," FWP fisheries biologist Kenny Breidinger told the Daily Inter Lake. "We take this one very seriously. There is a lot of potential for harm from brown trout in the drainage."
Both waters are hydrologically connected to the Flathead River, which is the problem. The upper drainage has stayed largely free of browns, and it holds Westslope cutthroat trout and federally threatened bull trout.
"In Ashley Lake and Church Slough, brown trout will compete for resources with and prey upon other sportfish," Breidinger said in an FWP release carried by Wired2Fish. "More concerning, both waterbodies provide a source for brown trout to spread throughout the Flathead Drainage. This would have substantial negative impacts on the Flathead fisheries."
Ashley Lake has no open outlet - Ashley Creek is blocked by a dam - which is why Breidinger believes the fish were put there deliberately. Biologists will now analyse the ear bones, or otoliths, of the recovered trout for trace elements that can be matched to specific streams, revealing where each fish was born. Their reproductive condition will indicate whether anything is spawning yet.
"If you know of anybody who's doing this or have any information that may be helpful in tracking down some of these criminals, it would be great to turn that into our law enforcement office and game warden," he told KPAX.
This is not the drainage's first scare. A brown trout was caught upstream of Pressentine Fishing Access in June 2025, and environmental DNA sampling afterwards found no trace of the species in the river. Jim Vashro, the former fisheries manager for FWP Region 1, told the Flathead Beacon that browns had already been introduced illegally into the Thompson and Kootenai rivers.
"Unfortunately, this latest detection isn't the only case where someone has moved brown trout around," Vashro said. "At this point, any detection of brown trout in the Flathead River has got to be some sort of bucket biology."
Mike Hensler, FWP's regional fisheries manager, framed the response around the natives when the 2025 fish surfaced: "Protecting our native trout populations is a priority. Brown trout pose a threat to native species in the Flathead drainage, and we need the public's help to manage this invasive species."
The awkward part for anglers is that brown trout are a prized sport fish almost everywhere else, including sections of the lower Flathead below SKQ Dam, where the dam contains them. Above it, the same fish is a management emergency.
It has been a rough summer for Montana more broadly. FWP has confirmed northern pike in the Three Forks Ponds within a mile of the Madison River, largemouth and smallmouth bass in Livingston's Sacajawea Lagoon, and pike in Pine Grove Pond near Kalispell - a stocked family trout fishery isolated from other waters, meaning someone carried them in. The agency is offering up to $3,500 for information.
"This is an extremely disappointing and damaging act," Hensler said of the Pine Grove introduction. "Pine Grove Pond was built and managed as a place for kids and families to learn to fish and enjoy catching trout. Introducing pike could ruin that experience for everyone."
Anglers who catch a brown trout in the Flathead drainage above SKQ Dam should kill it and call the FWP Region 1 office in Kalispell on 406-752-5501, with the date and location, and hand over the fish if they can. In lakes the fish may not look the part: instead of golden-brown with haloed spots, it can appear bright silver with a dark green back and large black spots.
