About the Project

Diversion 45 is a 10-foot-high by 8-foot-wide, concrete and steel agricultural diversion dam on the Big Wood River located within the city of Bellevue, Idaho and adjacent to the 36-acre Howard Nature Preserve. The largest diversion on the Big Wood River, it diverts 400 cubic feet per second of water to about 120 water users in Wood River Irrigation District 45 and the Triangle Irrigation District. Built in 1915 and reconstructed in the 1960s, it is failing 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.

Diversion 45 blocks access to the coldwater section of the Big Wood River suitable for trout. The dam prevents adults from migrating upstream to the coldwater refuge during the summer and fall when water levels are low, and year-round, juveniles and smaller fish are blocked from migrating upstream. Trout trapped downstream of Diversion 45 are unlikely to survive in the summer in the high water temperature.

Removal and replacement of Diversion 45 with a nature-like channel promotes migration of trout up and down the river corridor and into coldwater tributaries, allowing those fish to survive the hot summer months. It also promotes effective and safe agricultural water diversion to many Idaho farmers and ranchers. A modern diversion system will prevent the sediment buildup that impedes both water diversion and fish passage.

Fishing on the Big Wood River is a significant recreation draw for the region in the summer. The Department of Fish and Game estimates that recreational fishing brings in at least $10 million annually to the local economy, making fish habitat improvements important to the community. Species that will benefit from improved fish habitat and effective passage include several species of trout and native fish. The mainstem Big Wood River is used year-round by all age classes of trout.