KPAX Country

Sep 2, 2011 9:28 PM by Mark Holyoak (KPAX News)

Thompson Falls Dam now helping fish

THOMPSON FALLS- The "circle of life" is complete again after being blocked for almost 100 years.

When we stopped by recently, PPL Fisheries Brent Mabbott was measuring and weighing fish caught below the 32-foot high Thompson Falls Dam.

He used a 45-step, state-of-the-art, tallest of its kind in Montana, fish ladder that rises 72 feet from the Clark Fork River below. It was designed by and paid for, in full, by PPL Montana.

The numbers are astounding. PPL spent a million dollars in research on building the facility, then $7.5 million on construction. They also blew out 2,500 tons of rock and then laid down 1,600 cubic yards of concrete.

The ladder is the first of its kind in the Continental United States, built specifically to accommodate threatened bull trout. "We blocked the bull trout so we need to try to eliminate that block," Mabbott told us.

Of the approximately 1,600 fish that already climbed the ladder this year, very few are bull trout. "The fact that we only got two of them tells you the plight they're in. They're in trouble," Mabbott observed.

Here's how the 56-foot long ladder works. Fish are attracted to a small opening at its base by discharged water then once inside, they swim against a strong current. The individual steps, or pools, are five feet wide, about six to 10 feet long, and have openings at the top and bottom of each entrance.

"The ladder is not easy to negotiate. 45 different pods with six to eight cubic feet of water spilling through every one of them, so they're fighting velocity. The drive to go to their native streams is much greater than other outside factors," Mabbott explained.

The fish eventually reach the final 17-foot deep gathering pool. Working similar to an elevator, the water level rises and the fish come to the surface where they eventually flop their way toward a holding tank, where they're examined, the data recorded, and biologists inject what's called a "pit tag" into them so they can track the fish movements.

The day we visited the dam, eight fish made the trek, among them rainbow and brown trout, northern pike minnow and even a small mouth bass. They're then released above the dam and their journey complete.

"It works. We're getting fish over this thing. We took away the barrier for fish moving upstream," Mabbott said. "I've been a fisheries biologist for 35 years and it's fun to know we're making a difference here."

There are two fish biologists do not release into the Upper Clark Fork River, the walleye and lake trout. A lake trout climbed the ladder earlier this year, so Mabbott returned it back below the dam.

Contact Mark Holyoak


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