Ecosystem Responses to Dam Removal and Habitat Restoration in the Wind River, WA

Hemlock Dam was removed from Trout Creek, a Wind River, WA, tributary, in summer 2009 in order to improve the status of threatened wild summer steelhead populations in the watershed.  Dam removal returned a 2.6 hectare reservoir to river and improved steelhead passage, which previously depended upon a fish ladder. Ecosystem responses to dam removal, including fish populations, aquatic invertebrates, and physical habitat, are being documented as part of a multi-agency project initiated in the 1990’s to restore habitat in the watershed and monitor steelhead populations. Immediate changes to water temperatures, substrate composition, and aquatic invertebrate communities were observed in the former reservoir and immediately downstream, and these metrics now resemble measurements at reference sites. In contrast, fish population responses are ongoing due to biological time lags between the restoration action and its effects on various steelhead life history stages. Preliminary results suggest that adult and smolt abundance are increasing relative to reference areas.  Measuring fish responses to restoration is notoriously difficult; however, the existence of pre-dam removal abundance estimates and other biological data collected in the Trout Creek sub-basin and other sub-basins provide a unique opportunity to measure the responses of steelhead populations.