Rare Trout Being Studied at PPL Montana’s Thompson Falls Dam

Radio receivers mounted on PPL Montana’s Thompson Falls Dam are helping the survival of two rare species of trout on the Clark Fork River in a big way.

“We’ve been stepping up our collaboration with Montana Fish, Wildlife and Parks and the U.S. Fish and Wildlife Service to find a permanent solution to help bull trout and westslope cutthroat trout get a lift into their upstream native spawning waters,” said Brent Mabbott, PPL Montana’s senior fisheries biologist.

“Monitoring these species is not only important for regulatory compliance, but it’s the kind of project that represents the backbone of our company’s pledge to be responsible stewards of Montana’s rivers and environment,” he said.

The Clark Fork River at Thompson Falls was originally a natural waterfall, and westslope cutthroat trout — a species of special concern — the threatened bull trout, and other fish species would instinctively jump up the rocks to get upstream.

In 2001, PPL Montana installed a temporary 43-foot-long, 2-foot-wide ladder to a trap to help the fish reach the river on the upstream side of the dam. Fish captured in the trap could be trucked above the dam and released to assist in their passage to upstream locations.

By surgically implanting radio transmitters in the fish, they can be tracked during their migration and their approach toward the dam. This process is helping Mabbott and his staff and state fish biologists to come up with a recommendation for permanent passage for the trout.

The remote receiving stations on Thompson Falls Dam pick up the radio tag signals, and technicians also help track the migration of the fish. The radio receivers, about the size of 12-volt battery, are kept in a weatherproof enclosure and are powered by an 80-watt solar panel, which is connected to an antennae array.

Thompson Falls has many challenges when it comes to fish passage — the dam has two spillways, two powerhouses and a tributary confluence near its base, explained Laura Katzman, a Montana Fish, Wildlife and Parks fish biologist in Thompson Falls.

“The challenge is trying to find out a good site for a permanent trap or ladder,” she said.

“PPL Montana has been funding a fish technician who works with Montana Fish, Wildlife and Parks to assist with the fish passage study,” Katzman added. “PPL Montana is providing valuable resources for gathering information about fish passage at Thompson Falls Dam and is working with the state to attain the goal of permanent fish passage.”

Thompson Falls is one of two PPL Montana dams west of the Continental Divide. The Clark Fork River empties into the Columbia River, which in turn empties into the Pacific Ocean.