High water shuts down fish ladder

The trout are climbing, the trout are climbing, the trout are climbing! Well, they were until high water forced the ladder to close April 30.

According to Ryan Kreiner, Montana Fish, Wildlife & Parks (FWP) Fisheries Biologist, the ladder is closed when water flows reach 50,000 to 60,000 cubic feet per second (cfs). As soon as these levels normalize, the ladder will be back in action.

The recently reopened Thompson Falls fish ladder, Montana’s tallest at 48-vertical feet, has seen some action as trout begin their annual travels up the Clark Fork River.

Kreiner reported that a total of 65 fish have climbed the ladder this year. This total is comprised of 56 rainbow trout, six westslope cutthroat trout, two brown trout and one rainbow/cutthroat hybrid. The ladder is open for salmonid transportation services from late March through the end of October.

“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,” stated Kreiner.

The fish ladder is not constructed quite like an everyday ladder. Rather, within the coiling maze, fish swim through multiple pools roughly five feet wide and six to 10 feet long. The fish swim against a current of 6 cfs to attain their goal 356 feet later, at the exit gate. Since the Thompson Falls dam blocks passage for fish to reach their biological spawning locations, fish use the ladder to bypass the obstruction.

The fish ladder began operations in 2011. Since then, FWP reports that 16 bull trout have had successful ascents and passages, while two walleye have reached the summit, but denied passage.

FWP has determined an average of 380 trout ascend the ladder each year. Of this amount, it is estimated that 35 percent enter the Thompson River. This has biologists wondering where the remaining 65 percent go.

Currently, FWP is tracking the spawning and traveling behaviors of trout by implementing Passive Integrated Transponder (PIT) radio tags. In addition to PIT tag tracking, this year biologists are inserting Floy Tags. These tags are visible and contain a numerical identification number.

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

Anglers who catch a tagged trout are asked to report tag numbers and location of catch to FWP. So far this year, one tagged rainbow trout was reported up the Flathead River. Biologists declare that is it safe to consume fish with Floy Tags.

Since bull trout were officially listed as a federally threatened species 20 years ago, FWP has been devoted to conserving the salmonid. Warmer waters, deprivation of quality habitats, introduced structures, and competition with non-native fish species have all contributed to reduced bull trout populations, according to FWP.

The ladder is part of the Thompson Falls Hydroelectric Project, possible through collaboration between NorthWestern Energy, who owns the facility, and FWP, who handles operations. The ladder was the nation’s first full-height fish passageway designed specifically for bull trout and costed roughly $7.5 million.

Dam construction began in 1915 and took 650 men a total of 5 years to complete the 913-foot long structure. All materials used to build the dam were attained onsite. Of the three dams on the Clark Fork River, Thompson Falls is the oldest and smallest.