Bear River

Thomas Fork of the Bear River, ID/WY

Bonneville cutthroat trout currently occupy less than five percent of their historic range and the subspecies is designated as ‘Sensitive’ by the USDA Forest Service and ‘a Species of Concern’ by the states of Utah, Idaho, and Wyoming. The Thomas Fork of the Bear River supports the most genetically pure population of Bonneville cutthroat trout in Wyoming. Together with the neighboring Smith’s Fork and sections of the Bear River the systems comprises what is likely the last connected large river habitat available to migratory adult fish. Unfortunately, several diversion structures along the length of the Thomas Fork block upstream spawning migrations and divert downstream movement impacting Bonneville populations throughout the drainage. Trout Unlimited in partnership with the U.S. Forest Service, U.S. Fish and Wildlife Service, Idaho Department of Fish and Game, and Flyway River Ranch, are implementing plans to retrofit structures on the river with fish ladders and screens to ensure upstream fish passage during seasonal irrigation diversion. As part of this restoration effort, TU is monitoring the response of migratory Bonneville cutthroat trout to barrier removal in the Thomas Fork. Summer and fall fish movement data from both the Thomas Fork and Smith’s Fork, the neighboring reference stream, have been collected using two-way picket weirs since 2003.

Local project partners include the Idaho Department of Fish and Game, U.S. Fish and Wildlife Service, Flyway River Ranch, Upper Snake River Cutthroats Chapter of Trout Unlimited, Wyoming Council of Trout Unlimited, and Idaho Council of Trout Unlimited.

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