The Mayfield Dam downstream migrant fish facilities consisting of louvers and a bypass did not adequately guide juvenile migrant salmonids from water leading to the turbines. Attempts were made to improve the guiding efficiencies that included increasing the water velocities entering the bypass, simulating a wider bypass, screening part of the louvers near the bypass, and totally screening the louvers. Desirable results were achieved with total screening. Some of the interrelated factors influencing the guiding efficiencies of the downstream facilities were the reluctance of fish to readily enter the bypass, time of day, numbers of fish, size, and visibility. The variable factors affected all species in a similar manner.