Since its construction in the early 20th century, the Thompson Falls Dam on Montana’s Clark Fork River has posed a significant barrier to native fish migration. Completed in 1915, this hydroelectric facility continues to generate power but has inadvertently blocked fish, especially the threatened bull trout, from accessing hundreds of miles of upstream habitat.
Decades of observation revealed large numbers of bull trout congregating below the dam, unable to continue their natural upstream journey. Radio tracking further demonstrated that when these fish were manually transported above the dam, they traveled long distances toward suitable spawning grounds. This evidence underscored the urgent need for a solution that would restore natural passage for the species.
Innovating Passage for Bull Trout
Fish ladders are commonly installed at dams to facilitate salmon migration; however, the Thompson Falls Dam presented a unique challenge. Situated well beyond the migratory range of anadromous salmon, the dam required a fish passage tailored specifically to bull trout behavior and physiology. Complicating the effort was a lack of existing research on how bull trout would navigate such structures.
Engineers and biologists collaborated to devise a fish ladder capable of accommodating bull trout, an approach that had never before been attempted for this species. Their work represents a pioneering effort to reconcile hydroelectric power generation with the ecological needs of native fish populations.
By implementing this specialized fish ladder, the project has successfully enabled over 33,000 fish to move upstream, opening access to critical habitats that had been inaccessible for nearly 100 years. This achievement marks a significant milestone in balancing human infrastructure with environmental stewardship.