Fish ladder at Thompson Falls Dam dedicated

By Vince Devlin
Thompson Falls, Montana (AP) September 2010

Brent Mabbott says it was a curious sight, the fish they’d see leaping out of the water and onto rocks here.

The fish just wanted to do what comes naturally – swim upstream in the Clark Fork River, and into its dozens of tributaries to spawn.

One thing has stood in their way for the last 100 years. The 913-foot-long Thompson Falls Dam left fish vainly attempting to find a way around it.

Last week during the afternoon PPL Montana, operator of the dam, dedicated a new $7.5 million fish ladder that will allow fish – especially threatened bull trout – to go where they haven’t been able to for the last century.

“On behalf of myself, tribal people and our ancestors, I thank you,” said Tony Incashola, director of the Salish-Pend d’Oreille Cultural Committee. “It’s good to see people looking back and repairing some of the damages done in the past.”

The Confederated Salish and Kootenai Tribes, whose aboriginal territory includes these lands, joined forces with Montana Fish, Wildlife and Parks and the U.S. Fish and Wildlife Service to help PPL Montana – which paid for the ladder as part of its compliance costs for licensing – bring the project to fruition.

No one was happier than Pat Saffel, Region 2 fisheries manager for FWP.

It was Saffel who, as a fisheries biologist in Thompson Falls 10 years ago, used a net to catch fish and hand-carry them to the other side of the dam.

Saffel brought that very net with him to the dedication, then happily set it aside so he could juggle his notes and the microphone.

“Where once a guy was catching them one at a time,” he told the crowd, “we’re now on the brink of passing thousands of fish over the dam.”


It’s the first full-length fish ladder in the continental United States built specifically to accommodate the passage of bull trout, and the tallest facility of its kind in Montana.

The ladder is especially important to the survival of bull trout and westslope cutthroat trout, according to H. David Hoffman, director of external affairs for PPL Montana, and will open up hundreds of miles of the Clark Fork and its tributaries to those and other species.

The fish will use the “ladder” – it’s a bit like a lock system for fish instead of boats – to climb 75 feet and go from the bottom of the dam to the top (and back down, for those that return).

Years of research have gone into the design and construction according to Mabbott, PPL Montana fisheries biologist.

When fish were spied jumping onto the rock shelf below the dam, he says, “We said, ‘OK, we’ve got to see when they’re moving, how they’re moving, where they’re moving and how we can entice them to a ladder.”’

Fish were radio-tracked for three years. PPL Montana found it could attract fish to specific spots by opening certain gates on the dam.

“They’re attracted to the noise,” Mabbott says, and the new ladder can generate 20 cfs by its opening to lure fish to the right spot.

The company had previously constructed a 43-foot-long aluminum ladder on the rock shelf that was attached to a trap. For five years fish caught there were then trucked upstream and released.

“We had an eight-pound bull trout go up that ladder,” Mabbott says. “One night we had 1,200 fish in there.”

But high water wreaked havoc with the aluminum ladder – “One year we found it way downstream,” Mabbott says – and the solution remained a permanent passageway over the dam.

COP Construction of Billings removed 2,500 tons of rock to make way for the new facility, and poured 1,600 cubic yards of concrete to build it. The fish will gradually ascend and descend through 48 separate pools that gradually make their way up the face of the dam in something of a water-logged circular staircase.


For the next two or three years, once they reach the 45th pool, the fish will get something their ancestors never did on their travels past what is now Thompson Falls: an elevator ride.

As Mabbott explains, you don’t put in a $7.5 million fish ladder and then not track what, and how many, fish are using it.

So, when they reach the 45th pool, the fish will be diverted into a trap and lifted via an elevator to a platform with work stations.

There they’ll all be counted and classified, from suckers to bull trout.

Some will undergo genetics testing, be weighed and have scales taken to determine ages. PIT tags – passage integrated transponders – will be placed in some fins so biologists can track when they go up the ladder, and when they come back down.

Some will get radio tags so they can be tracked once they’re past the dam.

Once the work is done they’ll go back in a tank, a plug will be pulled and they’ll return to the ladder to complete their journey over the dam. All the time things like water temperature will be tracked to give officials an idea of when the ladder is most active, so they know what to expect in the future.

The ladder was filled with water for the first time last week. They’ll remove screens currently keeping fish out later this month and start testing things out, and anticipate a rush next spring.

“We’re confident we’ll get fish,” Mabbott says, “but how many, we don’t know. We may well have a wall of fish coming at us in April. Like Jon Hanson (a FWP fisheries biologist) says, we’ve got 100 years of fish stacked up back there.”