The spawning runs on Targhee and Howard Creeks historically produced about 70% of the wild-spawned fish in Henrys Lake. But access to the upper 16 miles of spawning habitat (including habitat for the revered Yellowstone Cutthroat Trout) in these creeks was effectively eliminated, as fish passage conditions through several culverts beneath State Highways 87/20 progressively worsened.

Water that flowed under Idaho 87 in both streambeds dropped more than a foot into an artificially straight channel that flowed into Henrys Lake. The small waterfall significantly impeded fish movement.

The project’s goal was to remove the barrier that was created when the existing structure was originally constructed. GeoEngineers’ initial stream assessment, recommendations and alternatives for stream enhancement design to correct the problem were the critical catalysts for moving the project forward. The magnitude, cost and urgency of this undertaking spurred the Henry’s Lake Foundation (HLF) to garner support, guidance and funding for the project from a number of regional non-profit organizations, state agencies and ITD.

The Idaho Transportation Board responded to this overwhelming and unprecedented support by passing a Special Resolution which ultimately funded the design and construction of the necessary bridges and stream enhancements in less than one year – a process which usually takes up to 10 years to complete. Restoration of the natural channels was placed on a fast track early in 2005; design work was completed in early June and construction was substantially completed by the end of the year. Formal completion of the new bridges and restored fish migration route was celebrated in June 2006.

This unprecedented effort may have saved Yellowstone Cutthroat Trout from inclusion on the Federal Endangered Species list. In place of the culverts is a 38-foot span across Howard Creek and an 80-foot clear span structure over Targhee Creek. The new design more closely replicates the natural flow and includes sands and gravels for stability and root wads, logs and other natural fish amenities. The creeks now flow gradually into a meandering channel that includes a series of riffles and pools, creating a “fish-friendly” environment.

This project demonstrates that it is possible to serve a transportation need and be environmentally sensitive at the same time. The project incorporated stream restoration components that went beyond the requirements needed to provide connectivity for Yellowstone Cutthroat to historic spawning habitat.