Montana Fish, Wildlife and Parks is proposing to waive angling limits on a lake in the Bob Marshall Wilderness that will become the next chapter in a multiyear effort to restore native westslope cutthroat trout.

Koessler Lake is scheduled to be treated with a toxin called rotenone this September to purge its existing fish population so that the lake can be restocked with genetically pure westslope cutthroats.

It’s part of the South Fork Flathead Cutthroat Conservation Project, which has involved systematically removing non-native and hybrid fish from alpine lakes above the South Fork Flathead River drainage.

The South Fork is considered a stronghold for westslope cutthroats, a fish that has been in decline in other Montana waters.

Project biologist Matt Boyer said that since 2007, 12 lakes have been successfully chemically treated and an additional six lakes have been “swamped” with high numbers of genetically pure trout. Only three lakes remain on the original list of 21 encompassed by the project.

Boyer is encouraged by the project accomplishments.

“The gains that have been made for westslope cutthroat trout and the South Fork Flathead fishery area tremendous benefit for the resource,” he said. “The partnerships made along the way will pave the way for more conservation successes into the future.”

He said the project, which is paid for by Bonneville Power Administration mitigation money, has involved a great deal of effort that has involved the U.S. Forest Service and groups such as Back Country Horsemen and Trout Unlimited.

Montana Fish, Wildlife and Parks has conducted hundreds of amphibian, plankton and aquatic insect surveys to document species composition and population recoveries after rotenone treatments.

Over 11,000 miles of trail have been hiked or ridden on horseback to conduct surveys, to carry out rotenone treatments and collect will fish to develop source stocks for repopulating the lakes.

Almost a half million westslope cutthroats have been stocked in the lakes after they’ve been treated, and Boyer said that fishery population recoveries have been rapid, one of the project’s major goals.