Pettit Lake Creek Weir

Pettit Lake Creek Weir

Pettit Lake Creek Weir

An Effort to Save the Snake River Sockeye

In the 1960s, after propagating the Snake River for centuries, the Snake River sockeye salmon were blocked from their historic breeding grounds in Pettit Lake. As their populations dwindled over the next 30 years and the Shoshone-Bannock Tribe petitioned for listing on the Endangered Species List, the species teetered on extinction. Despite the blockage removal, habitat improvements and a captive breeding program, the previous Pettit Lake Creek Weir remained an obstacle. 

The new weir fixes a design flaw — one that miscalculated the creek’s peak flow — while its innovative design is friendlier for fish and the tribe. It traps both juveniles and, for the first time, adults. It uses stainless steel boxes and during the fall season, the boxes will be raised straight up out of the water for adult salmon trappings. Grooves on the structure allow picket panels to be placed in each bay, allowing the adult salmon to navigate their way to the head gate and into the adult trap box. The trap box is 6 feet deep with a pulley floor system and can hold up to 50 adult salmon. There will also be a cascading flow from the creek into the head box and trap box. It will help biologists gather data and tag the fish, which will have far-reaching impacts on restoring the population. 

After two years of growing in the lake, the fish begin a two-year, 1,800-mile round trip to the Pacific Ocean and back — the longest and highest distance to travel for any fish. The project — and plan — provides for a healthy future for sockeye in Redfish, Pettit and Alturas lakes. The effort began in Redfish lake, which is now operational, and much of the focus has transitioned to Pettit. However, when Pettit is trending toward recovery, the team and tribe will begin looking toward other lakes that historically had sockeye salmon in them. 

At one time, more than 150,000 sockeye salmon returned to central Idaho. When the Shoshone-Bannock petitioned for protected status, there were just four. Since then, populations have stabilized, but the new weir begins a process in restoring the sockeye populations that once swam through the creek. Less intrusive than the previous structure, it is in the same location but can handle increased flows, does not collect debris and blends into the area. The precast concrete and weathered steel structure simplified construction, reduced impacts and maintains the Sawtooth National Recreation Area’s visual requirements. 

The project team worked alongside the Shoshone-Bannock Tribe, Bonneville Power Administration, U.S. Army Corps of Engineers, Idaho Department of Fish and Game, and the U.S. Forest Service to deliver the one-of-a-kind project. Constructed through the summer while the creek levels were low, the project team completed the project prior to the annual migration. 

Completed on budget and on schedule, the new weir marks a key point in the critical restoration of the tribe and region’s biological and cultural heritage. 
 

Pettit Lake Creek Weir
Client
Shoshone-Bannock Tribe
Location

Blaine County, ID
United States

Markets

Awards

First Place Award (2022)
Engineering Excellence Awards
American Council of Engineering Companies of Idaho
Grand Award (2022)
Engineering Excellence Awards
American Council of Engineering Companies