Chemical-specific and toxicity based approaches were used to assess effluent and receiving water quality of Monroe Harbor, Michigan. Toxicity was defined and measured by bioassay techniques using water both from control sites and points of impact. Inhibition of bacterial decomposer activity, phytoplankton productivity, zooplankton reproduction and grazing efficiency, survival of zooplankton and larval fish and contaminant accumulation were measured. An undetermined loading of PCBs approaching 200 g/day in the Lower Raisin River was found by using an input-output mass balance model. An attempt was made to integrate the toxicity based and chemical specific approaches. Zinc and copper appear to be toxic to different species and to affect specific ecosystem functions, either singly or in combination. Although PCBs were important in the bioaccumulation studies, they did not appear significant in describing observed toxicity in the Ceriodaphnia reproduction and survival in the seven day Mount-Norberg life cycle test.