State wildlife officials are seeking help to combat the suspected infiltration of nonnative brown trout into the Flathead River drainage.

Montana Fish, Wildlife and Parks confirmed the presence of brown trout in Ashley Lake after reviewing photos taken by an angler in February. The fisherman told officials he was unsure what he had reeled in and released the fish after photographing it.  

A second brown trout was later caught in Ashley Lake and provided to state fisheries biologists for analysis. Another angler shared photos with the state wildlife agency of a brown trout he said he caught in Church Slough earlier this week. 

“This is a big deal,” said Kenny Briedinger, a fisheries biologist with Montana Fish, Wildlife and Parks. “We take this one very seriously. There is a lot of potential for harm from brown trout in the drainage.” 

While state officials stock the prized sportfish in some waterbodies, brown trout are considered an invasive species in Northwest Montana. The trout preys upon some native species of fish and competes with others for food and other resources. 

The detections at Ashley Lake and Church Slough are especially concerning, said Breidinger, as both waterbodies are hydrologically connected to the Flathead River.  

Last summer, a photo surfaced of a brown trout supposedly caught in the Flathead River upstream of Pressentine Fishing Access Site in Evergreen. No landmarks were visible in the photo, so officials were unable to verify the authenticity of the report. Subsequent testing for traces for brown trout DNA in the Flathead River turned up nothing. 

Briedinger said he feels “very confident” about the veracity of the brown trout observations in Ashley Lake because the photos provided to officials included identifiable landmarks. He posited that the fish were illegally introduced, as the only outlet from the lake — Ashley Creek — is blocked by a dam. 

Fisheries biologists will analyze the ear bones of the brown trout handed over to the state wildlife agency for trace elements, which can then be mapped to specific streams to determine where a fish was born. That information, along with observations on the trout’s reproductive status, will help officials determine whether the brown trout population in Ashley Lake has become established enough to reproduce. 

The state agency is urging anglers that catch a brown trout in the Flathead River Drainage upstream of the SKQ Dam to kill the fish and report their catch to the Montana Fish, Wildlife and Parks Region 1 office at 406-752-5501. Anglers will be asked to submit the brown trout to fisheries biologists for analysis. 

Brown trout can typically be distinguished from other trout species by their golden brown or yellow-brown color and dark spots surrounded by lighter halos. In large waterbodies, including Ashley Lake, brown trout may instead appear silvery with a dark green back overlaid by large dark spots.