After restoration by whole-lake applications of liquid aluminum sulfate, Medical Lake, Washington, received a total planting of approximately 31,000 fingerling rainbow trout (Salmo gairdneri) from 1978 to 1980. Prior to treatment the lake had been unable to support game fish. Post-treatment improvement in water quality and zooplankton standing crops permitted good trout survival and growth.Daphnia pulexcomprised over 90 percent of the trout diet for most age classes and dominated the biomass of the 0+ age class.