AbstractIn the laboratory, preference/avoidance behavioral testing was used to investigate the potential of both domestic and industrial waste discharges to interfere with the migration of anadromous fish. Various dilutions of the effluents were tested using the behavioral response of fish as measured by linear velocity, locational position and other factors. A video‐based computerized system was used to capture and analyze the behavioral data in real time. Test species were chinook salmon,Oncorhynchus tshawytscha, striped bass,Morone saxatilisand steelhead,Salmo gairdneri.Dilution rates were established based upon dye studies and waste field dispersion modeling. Dilutions down to 1,000:1 were tested and evaluations of the potential for each discharge to affect fish migrations were made. Both attraction and avoidance responses were observed at different concentrations of the discharges studied. Test fish exhibited strong responses at levels as low as 1,000:1 of effluent. Laboratory behavioral data were compared with field surveys where possible. A discussion of behavioral testing as a tool to assess the potential effects of discharges on fish migration is presente