News & Features

Life Returns to a Poisoned Lake

Blackfoot Lake

Blackfoot Lake sits at the bottom of a Jewel Basin mountainside, surrounded on one side by the limbless, charred tree spikes left over from a 2003 wildfire, and on the other by thick, green evergreens. Today, the fish are jumping.

“There’s a rise, and another one, oh yeah John, they’re here,” Montana Fish Wildlife and Parks biologist Matt Boyer said. He and his colleague John Fraley hiked up to the lake to collect what will probably be the last samples of the season.

A year ago, in early October 2007, Blackfoot was treated with the poison rotenone as part of the South Fork Westslope Cutthroat Trout Conservation Project. For two years before the treatment, Boyer and other fisheries biologists collected insect, plankton, and amphibian samples. They then treated the lake with the poison; killing off the Yellowstone-Rainbow Trout hybrids living there as well as most of the insect and amphibious life. This past spring, they restocked the lake with genetically pure westslope cutthroat trout from the Anaconda Hatchery.

“Everything’s back to what it was pre-treatment,”Boyer said. “The major difference is the size of the fish.” Boyer says the hybrids measured 17 to 18 inches before the poisoning. FWP restocked with two ages of fish that range in size from about 5 inches to 12 inches.

In addition to catching fish and noting their coloring and size, Boyer is tracking what’s living around the edges of the lake, in its depths and on its surface.

“That type of stuff is every bit as important as the fish,” Boyer said. “If the ecosystem is not healthy, if there’s not food for the trout – you can’t manage for just one.”

Blackfoot Lake is one of the lakes poisoned in the fall of 2007 to get rid of non-native, hybrid trout as part of the South Fork Westslope Cutthroat Trout Project.

As Boyer crouched in the outlet of the lake, he set up a filtering net to catch insects from the water. He lifted up rocks, flushing out the mayflies, caddisflies and stoneflies. From this outlet, the water flows down and hooks up with water flowing out of another treated lake, Black Lake at Graves Creek. It then flows down toward Handkerchief Lake, into the Hungry Horse Reservoir, and down into the South Fork of the Flathead River.

The poisoning project initially started because the hybrid trout in the Jewel Basin lakes were starting to show up downstream. Boyer says historically the lakes in the Jewel were barren because the falls above the lakes in the South Fork blocked fish from coming up. But in the late 1920s, through the 30s and 40s, people were encouraged to pack fish up to the lakes and non-native Yellowstone cutthroat and rainbow trout began to thrive.

“So a fish was a fish,” Boyer said. “If it tugged on the end of a line, great.” He said the South Fork of the Flathead is considered a stronghold for native westslope cutthroats, and argued that’s why it was so important to do the treatments now, when they had just a few reports of hybrids making their way into the drainage.

Much of the opposition to this project comes from backcountry outfitters. For them, they’re losing the big fish their clients were catching.

“The present fish in these lakes are thriving, healthy fish,” states a letter written by Virgil and Barb Burns, owners of the Bob Marshall Wilderness Ranch. “Fishing for these ‘exotic’ fish is excellent. Why should anyone be allowed to tamper with these healthy fish in order to obtain a genetically pure strain of fish?” If anything, Burns wrote, swamping the lake with westslope cutthroat is the best choice.

Swamping involves stocking a lake with copious amounts of a particular species. Boyer says swamping works in some lakes but not in others. Blackfoot Lake, he said, was swamped with westslope cutthroat on and off for two decades.

“It still contained fish that were basically pure rainbow,” Boyer said. Woodward, Pyramid, and Pilgrim Lakes, on the other hand, Boyer said went from pure Yellowstone cutthroats and rainbows to 95-percent pure westslope cutthroats.

Next year, FWP will be back, collecting samples to see if life in the lake is continuing to regenerate. Big Hawk Lake will be treated with rotenone this fall, as will a portion of Graves Creek, terminating at the barrier falls above Handkerchief Lake.

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