Passage Mitigation at Main Stem Columbia River Dams - How Well Is It Working

A series of thirteen run of the river hydroelectric dams were built on the mainstem Columbia and lower Snake Rivers between 1930 and 1975 which were intended to allow continued passage of anadromous fish. Access to the upper portions of the basin was blocked by high head storage dams which are not fitted with passage provisions. This review traces the experience of resource managers with structural passage facilities and related mitigative measures at medium head hydroelectric dams for upstream migrating adult salmon and steelhead (Oncorhynchus spp.) and downstream migrating juvenile fish. Trends in upriver populations of salmon and steelhead and possible factors contributing to current population levels are discussed. Three phases in the development of management objectives are identified and success at meeting objectives is evaluated. Consequences of evolving management strategies, future management requirements, and options for the further development of passage mitigation measures are summarized