Big Wood River

Diversion 45 is an agricultural diversion dam on the Big Wood River that lies within the city of Bellevue, Idaho and abuts the 36-acre Howard Nature Preserve. The 100-foot-long by 8 foot wide by 10-foot-high concrete and steel dam diverts 400 cubic feet per second of water, making it the largest diversion on the Big Wood River. It supplies water to about 120 users in Wood River Irrigation District 45 as well as the Triangle Irrigation District. The dam was built in 1915 and reconstructed in the 1960s, but is no longer functional due to sediment accumulation and channel migration. In order to divert water, the dam’s owner, Wood River Irrigation District 45, uses heavy equipment annually to sculpt the channel and sediment to create push up dams. In 2017, 2000 cubic yards of sediment were removed in a futile attempt to restore functionality.

Diversion 45 acts as a barrier to adult fish migration upstream during the lower flow part of the year, and a complete barrier to upstream migration for juvenile fish. The best summer habitat lies upstream because, in low flow periods, much of the river’s flow is diverted at Bellevue. Species that will benefit from effective passage include redband, rainbow, and introduced brown trout, as well as mountain whitefish and the endemic Wood River sculpin. For trout, the mainstem Big Wood River is used by all age classes year-round, with migration up and down the river corridor and into tributaries.

Fishing on the Big Wood River is a significant recreation draw in the summer, with the Department of Fish and Game estimating that recreational fishing brings in at least $10 million annually to the local economy. Improving fish habitat and recreational fishing is important to the community.