PROJECT OVERVIEW​

For more than a century, an aging diversion dam on the Big Wood River near Bellevue has directed water into the Diversion 45 Canal, supplying roughly 9,000 acres of farmland across the Bellevue Triangle. But the same structure that keeps water flowing to local growers has also stood as a barrier to fish passage, cutting off habitat above and below the dam for generations of trout.
 
Construction began in August 2026 on a restoration project designed to solve two problems at once: keep the dam functioning safely for irrigation, and reopen the river to unimpeded fish passage for the first time in decades.

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RESTORATION STRATEGIES

• Filling a scour hole below the dam with gravel and newly placed boulders to stabilize the riverbed

• Reshaping the stream bed below the dam into a graded ramp rather than a vertical drop, so fish can move up and downstream

• Cutting a notch into the dam itself to allow fish passage

• Placing rock and wood downstream to control erosion and stabilize the channel

• Temporarily diverting river flow around the dam during construction, while maintaining a minimum flow of 50 cubic feet per second at all times, per an agreement between Irrigation District 45, the Triangle Irrigation District, Project Big Wood, and Trout Unlimited

• Revegetating all areas disturbed by construction

Because the dam must be completely dry during construction, some fish will be stranded below the dam as water is temporarily rerouted around it through D45. Project Big Wood and Trout Unlimited volunteers are conducting fish rescues throughout construction to safely relocate fish as needed.

Construction began August 10, 2026 and is expected to be complete by November 2026.

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PROJECT GOALS AND BENEFITS

• Reconnect fish habitat: Restore fish passage above and below the dam

• Protect irrigation delivery: Secure the water supply for roughly 9,000 acres of farmland in the Bellevue Triangle

• Reduce failure risk: Repair aging infrastructure before it fails

• Stabilize the riverbed: Reduce erosion and scour immediately downstream of the dam

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PARTNERS

This project is a partnership between Irrigation District 45, the Triangle Irrigation District, Trout Unlimited, and Project Big Wood, with engineering by J-U-B Engineers and construction by Schreder and Brandt. It is funded in part by a grant from the Idaho Department of Water Resources, a WaterSMART grant from the Bureau of Reclamation, a State Agricultural Best Management Practices grant secured by Project Big Wood, and a contribution from Trout Unlimited through the OpenWaters Fund.