Montana's tallest fish ladder is back in action

In a gradual journey up the lower Clark Fork River, trout are once again ascending the tallest fish ladder in Montana.

Climbing 48 vertical feet, the upstream fish passage facility, or fish ladder, is part of the Thompson Falls Hydroelectric Project in northwest Montana. The full-height facility, owned by NorthWestern Energy and operated cooperatively with Montana Fish, Wildlife and Parks, runs from late March to the end of October.

In the first month since the ladder reopened this spring, more than 50 large rainbow trout, two brown trout and five westslope cutthroat trout have already achieved documented ascents.

On average, approximately 380 trout successfully ascend the ladder each year, of which 35% typically enter the Thompson River just upstream of the dam.

Since the facility opened in 2011, 16 bull trout have successfully ascended into the upper stretches of the Clark Fork.

Two walleye have climbed the ladder but denied passage.

“This ladder was designed to benefit the native salmonids, primarily bull trout, but we also want to learn what contributions the ladder may have for recreational fisheries.” said FWP Biologist Ryan Kreiner.

Using Passive Integrated Transponder (PIT) tags, fisheries biologists are tracking the movements of trout to better understand spawning and traveling habits.

Continuing in 2018, biologists are also inserting visible Floy Tags into all trout to obtain angler catch data.

An estimated 35 percent of trout that ascend the Thompson Falls fish ladder enter the Thompson River and biologists are curious where the remaining 65 percent are traveling.

One tagged rainbow trout has already been reported up the Flathead River.

Anglers who catch a trout with a Floy Tag are asked to please contact FWP to report the location. It is safe to consumer fish with Floy Tags.

“We want anglers to help us figure out where these trout are going,”said Kreiner.

The Thompson Falls ladder was the nation’s first full-height fishway designed specifically to accommodate the passage of bull trout.

The structure was built because Thompson Falls Dam was adversely affecting threatened bull trout and a fish ladder would reduce, but not eliminate, the impacts of the hydro project.

The dam, commissioned in 1915, is the oldest and smallest of three on the Clark Fork River.