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9 months after a single brown trout {photograph} triggered certainly one of northwest Montana’s most pressing fisheries investigations, Montana Fish, Wildlife & Parks says eDNA testing discovered no hint of the nonnative fish—however the company isn’t standing down. As guides and anglers return to the Flathead River drainage this spring, FWP continues to be asking everybody on the water to kill any brown trout caught and produce the fish to the Area 1 workplace in Kalispell.
The Detection That Began It All
In early June 2025, a neighborhood information reported {that a} shopper had landed a brown trout on the Flathead River between Pressentine and Teakettle fishing entry websites close to Evergreen. The information photographed the fish, confirmed the kill, however didn’t maintain the carcass—eliminating any probability for biologists to look at the fish’s otolith and hint its origin. FWP confirmed the detection via press release on July 14, 2025, and the investigation was on.
The Flathead River drainage above SKQ Dam—the Séliš Ksanka Ql’ispé Dam on the outlet of Flathead Lake—has been fastidiously guarded as a stronghold for native westslope cutthroat trout and federally threatened bull trout (Salvelinus confluentus). Brown trout under the dam are frequent; above it, the impoundment has functioned as an impassable barrier to pure upstream migration for many years. The one believable rationalization for a brown trout above the dam, mentioned FWP Fisheries Administration Biologist Kenny Breidinger, was human intervention.
Jim Vashro, former fisheries supervisor for FWP Area 1, famous that brown trout have already established themselves within the Thompson River and the Kootenai River downstream of Kootenai Falls by way of unlawful introductions. “At this level, any detection of brown trout within the Flathead River has acquired to be some form of bucket biology,” he mentioned.
What eDNA Discovered—and Didn’t Discover
To gauge the scope of the intrusion, FWP collected water samples from 13 websites between Previous Metal Bridge and Teakettle Bridge, processing them for hint genetic materials from brown trout. The samples, analyzed at an outdoor laboratory, got here again unfavorable throughout the board.
The percentages of an eDNA hit scale with inhabitants dimension: a self-sustaining breeding inhabitants would nearly definitely depart a sign. 13 consecutive misses supply significant reassurance.
“We’re hopeful that there’s not a brown trout inhabitants within the river,” Breidinger informed the Daily Inter Lake in February 2026. He additionally acknowledged uncertainty concerning the unique report itself. The information’s {photograph} was angled towards the underside of a ship with no seen landmarks, and Breidinger mentioned he was by no means capable of totally affirm the fish was caught the place reported. “We by no means had been capable of affirm this was a reliable report,” he mentioned.
That ambiguity cuts each methods. If the report was correct, the fish might have been an remoted particular person somewhat than the forefront of a longtime inhabitants. If it wasn’t caught within the Flathead drainage in any respect, the risk stage drops additional. Both approach, FWP shouldn’t be declaring the case closed.
Why the Menace Nonetheless Issues
Brown trout pose layered issues for native salmonids. They outcompete westslope cutthroat trout and bull trout for meals and holding water and prey actively on juvenile fish. Breidinger additionally famous that as a result of brown trout typically spawn in fall simply after bull trout in most of the identical tributaries, they’ve been recognized to disturb native redds.
The drainage has survived a brush with this earlier than. Greater than 25 years in the past, brown trout escaped from the Creston Nationwide Fish Hatchery into Mill Creek, a Flathead tributary. FWP mounted a suppression effort that, over a number of years, appeared to get rid of the fish earlier than a breeding inhabitants might take maintain. Subsequent eDNA checks in Mill Creek discovered no brown trout. The company’s response to the 2025 detection drew immediately on that playbook.
“If there have been a reproducing inhabitants of brown trout, I feel we might learn about it,” Breidinger mentioned in July 2025. “We’re fairly assured that this was a results of an unlawful introduction and never from some unknown inhabitants.”
Shifting stay fish between Montana waterbodies is unlawful. Violations may end up in fines, imprisonment, and forfeiture of fishing and looking licenses.
What Anglers Ought to Do
FWP’s standing directive for the Flathead drainage stays in impact: any brown trout caught within the Flathead River or its tributaries have to be killed instantly. Anglers ought to retain the fish and get in touch with the FWP Area 1 workplace in Kalispell at 406-752-5501, offering the date and precise location of the catch.
Brown trout are identifiable by their golden brown to yellow-brown coloration, darkish spots typically ringed by pale halos, and occasional purple or orange spots.
“Defending our native trout populations is a precedence,” mentioned FWP Regional Fisheries Supervisor Mike Hensler. “Brown trout pose a risk to native species within the Flathead drainage, and we want the general public’s assist to handle this invasive species.”
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