Actions have been taken to replace diversion dams in lower Beaver Creek with a series of rock vortex weirs. Some of these diversion dams have been in place for over 100 years, and they have impaired or completely blocked upstream migration of fish. Three diversion dams were replaced in 2003 (Lower Stokes, Thurlow Transfer, and Upper Stokes), and a forth diversion dam was replaced in 2004 (Fort-Thurlow). These vortex weirs were designed and installed under the supervision of U.S. Bureau of Reclamation (BOR) engineers and completed in accordance to National Marine Fisheries Service (NMFS) and Washington Department of Fisheries and Wildlife (WDFW) fish passage criteria. The projects were designed to meet fish species recovery needs described by the Endangered Species Act (ESA) and the “BiOp” issued by NMFS (2000a). Since no specific guidelines have been identified to date specifically addressing diversion dams, WDFW and NMFS guidelines are being considered as the target design and performance criteria for the sites monitored as part of this project. Where used, the vortex weirs were designed to maintain irrigation diversion capabilities while improving fish passage.