Middle Lemhi River – Hayden Reach Phase 2

The Idaho Department of Fish and Game (IDFG) will implement Phase 2 of the Middle Lemhi River Hayden Reach project. Funds will support design and construction of habitat treatments on a 0.25 mile segment of the Lemhi River located near the confluence of Hayden Creek and the Lemhi River. Because of its relatively large scale, this project was partitioned into three project phases. Phase 1 (006 20 SA) construction will begin in early November 2022. Phase 2 will build upon Phase 1 efforts to re-establish a more functional floodplain. Phase 3 funds will be pursued in subsequent PCSRF rounds.



Current conditions include a straightened channelized river segment confined by State Highway 28, containing no instream woody structure, no side channels or other lateral habitat, and a disengaged floodplain. Project actions include: 1) realigning the Lemhi River to increase sinuosity, reducing slope and current velocities, 2) grading the existing banks and raising the surface water of the river by installing engineered riffles to increase lateral inundation of the floodplain, 3) installing engineered log jams, bank roughening structures, and other woody debris structures to provide channel complexity and roughness, and 4) revegetate disturbed areas to promote riparian zone recovery.

Middle Lemhi River – Hayden Reach Phase 2 project actions will continue to focus on developing a more complex and natural floodplain. Increasing river sinuosity, developing habitat complexity in the form of woody debris structures, constructing side channels, and riparian zone restoration will translate into increased habitat capacity for juvenile life stages of salmon and steelhead. Expected fish response includes improved survival for all freshwater juvenile life stages. Furthermore, the magnitude of these affects will be substantial since the project is located at the downstream end of the Lemhi primary Chinook salmon production area. Immediately upstream of the project site, the Lemhi River is a heavily incised single thread channel with no functional summer rearing or wintering habitat. As such, the project is ideally located to function as a “catcher’s mitt”, providing much needed habitat for rearing parr that were displaced by spring high flows from upstream production areas, and for pre-smolts moving out of the production areas in the fall in preparation for overwintering.