Summary: The louver-type fish screen at the U.S. Bureau of Reclamation's Tracy fish collection facility was developed by the U.S. Fish and Wildlife Service and the U.S. Bureau of Reclamation, and shortly after being put into operation in 1957, was tested by them to determine its efficiency at deflecting fish. This screen includes a large primary louver system and a much smaller secondary louver system. Test results of the primary louvers in 1957 were inconclusive, but in 1958 and 1959 the efficiency of the secondary louver system was determined to be at least 90 percent, meaning that 90 percent or more of the fish which encountered this system were diverted in the manner desired, and 10 percent or less went through the screen and into the canal.