Walla Walla River Basin Fish Screen Evaluations; Nursery Bridge Fishway, Garden City/Lowden II, and Little Walla Walla Sites, 2004 Annual Report.

Pacific Northwest National Laboratory evaluated the fish screens at the Nursery Bridge Fishway, the Garden City/Lowden II site west of Walla Walla, Washington, and the Little Walla Walla site in Milton-Freewater, Oregon, in the Walla Walla River Basin during 2004. The fish-screen facilities were examined to determine if they were being effectively operated and maintained to provide for safe fish passage. At the Nursery Bridge Fishway, the screens were evaluated specifically to determine whether the louvers that aid in controlling water flow from behind the screens could be adjusted so that the screens would meet fish-protection criteria. Data were collected to determine whether velocities in front of the screens met current National Oceanic and Atmospheric Administration's National Marine Fisheries Service (NOAA Fisheries) (formerly NMFS) criteria to promote safe and timely fish passage before and after changing the louver settings. The Little Walla Walla screens were evaluated to determine how a build-up of algae on the screens affected water velocities.