Glacier National Park officials are moving forward with plans to introduce cutthroat and bull trout into Gunsight Lake.

According to a release from park officials, the regional director for National Park Service Interior Regions 6, 7 and 8 recently signed off on findings that there were no significant adverse effects from the project, which will remove non-native rainbow trout and replace them with westslope cutthroat trout, bull trout and mountain whitefish.

The Environmental Assessment for the project argued that both trout species are native to the park and that moving them into Gunsight Lake will protect them from the threats of hybridization and climate change. Ongoing hybridization with non-native rainbow and Yellowstone cutthroat trout is occurring in almost every westslope cutthroat population in the St. Mary River drainage. Though mountain whitefish are native to the park, they were omitted from the original project proposal.

Gunsight Lake presents an opportunity to establish native fish habitat secure against hybridization, officials concluded. Once removed, non-native species are prevented from entering the lake owing to downstream waterfalls that prevent upstream fish migration, according to the park’s Environmental Assessment.

Non-native rainbow trout will be removed from the lake using an EPA registered and approved fish toxicant, rotenone. While rotenone degrades naturally with sunlight and water movement, detoxification will be hastened with a neutralizing agent, officials said.

The neutralizing agent, potassium permanganate, is widely used for the treatment of municipal drinking water and wastewater. Both rotenone and potassium permanganate dissipate with no detectable long-term changes to water quality.

Following the removal of the non-native rainbow trout, genetically pure westslope cutthroat trout, bull trout and mountain whitefish will be translocated into Gunsight Lake.

FRIENDS OF the Wild Swan Program Director Arlene Montgomery is among leaders of several environmental groups who spoke out against the project during its public comment period.

A letter sent to the National Park Service in June by the groups protested the use of helicopters and other motorized equipment for the undertaking. They also objected to restocking the lake at all, claiming it was fishless before it was stocked with rainbow trout decades ago, as reported by the Hungry Horse News.

Montgomery said the decision is disappointing, noting that the original proposal did not include the introduction of mountain whitefish. She believes the project is experimental, particularly because it involves moving established native fish populations that are vulnerable.

“They’re going to be putting in three species of fish that were never in that lake,” Montgomery said. “... There’s no guarantee that it will be successful and it’s just not a place to be playing around or tinkering with an ecosystem.”

Wilderness Watch Executive Director George Nickas also signed the June letter to the park service. He said the group disagreed with the park’s approach.

“These trout-centric plans that all these fishery biologists are pursuing are not in the best interest of park or biodiversity conservation. They’re focusing on single species to the detriment of the natural ecosystem,” Nickas said. “So generally speaking, we don’t think they should be going forward with this particular plan.”

According to the Environmental Assessment, climate change compounds the stressors to native trout species in Glacier. This includes changes in stream flow and warmer water temperatures, which stress fish, degrade their habitat and favor non-native species. Because of its high elevation, Gunsight Lake has a high likelihood of sustaining the cold-water habitat necessary for westslope cutthroat and bull trout to persist in a changing climate.

Project activities will begin in late August or early September of this year. The treatment area will be temporarily closed to the public during rotenone application and detoxification. The park anticipates closing Gunsight Pass Trail for about one week around the site preparation and rotenone treatment application period. The closure will extend from Reynolds Campground junction and just east of Gunsight Pass.

Gunsight Lake wilderness campground will close Sept. 1, 2023, until next spring. Project funding is being provided by the National Park Service Natural Resources Preservation Program and the Glacier National Park Conservancy.

More detailed information on the project, including the Environmental Assessment, Finding of No Significant Impact and a Minimum Requirements Analysis, is available on the NPS Planning, Environment & Public Comment website.

Reporter Taylor Inman can be reached at 406-758-4433 or by emailing tinman@dailyinterlake.com.