Thompson Falls fish ladder will help rare trout species

Artist’s rendering of the proposed Thompson Falls fish ladder (background) in the main channel of the dam.

PPL Montana plans to build a permanent fish ladder at its hydroelectric dam at  Thompson Falls, giving two rare species of trout safe passage into their native spawning waters upstream on the Clark Fork River.

“As part of our federal operating license and our commitment to fisheries and river  resources, PPL Montana has filed formal plans for a permanent fish ladder at Thompson Falls,” said Jon Jourdonnais, PPL Montana’s director of hydro licensing and environmental compliance.

“This project is significant because it will reopen hundreds of miles of the upstream Clark Fork River and its tributaries for bull trout, westslope cutthroat trout and other fish,” Jourdonnais said.

Pending approval of the proposal by the Federal Energy Regulatory Commission, construction on the $6 million project is expected to begin in spring of 2009 and be completed in 2010. The project will be funded entirely by PPL Montana.

The fish ladder — which will replace an experimental, temporary fish passage system used since 2003 — will have 47 individual step pools, each filled with water, that will gradually ascend about 75 feet to the top of the dam. Fish will swim their way through the individual pools until they get over the dam.

PPL Montana will place the new system on the north side of the main channel, where years of fish behavior and tracking studies have determined fish congregate below the dam.

“This innovative design will attract the fish by having water cascade down the ladder at the dam, causing them to move instinctively toward and into the fish passage system,” he said. “Our goal will be recovery of bull trout, which is endangered, and westslope cutthroat trout, a species of special concern.”

There will be a mechanical lift that can be used as needed as part of the ladder operation, where biologists can radio tag and examine the fish, near a spot where the public may view the ladder operations.

The Clark Fork River at Thompson Falls was originally a natural river falls, and fish would instinctively jump the rock cascade to get upstream.

“PPL Montana’s leadership and commitment to protect the endangered bull trout and other species are commendable,” said Chris Hunter, chief of fisheries with Montana Fish, Wildlife and Parks. “This project will provide so many benefits to the state of Montana with regards to healthy fish conservation and helping manage healthy native and sport fishing within the Clark Fork River Basin.”

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