Because the Provincial Water Quality Objectives for ammonia are exceeded for the length of the upper Serpent River downstream of the industrial effluents during certain periods of the year, it is inappropriate to define mixing zones. Due to the periodic presence of ammonia concentrations potentially lethal to fish, the immediate rehabilitation of the upper Serpent River is not a viable option with the existing process technology. It is recommended that the investigation of an alternate process technology that would significantly reduce in-stream ammonia concentrations be initiated. Realizing that stress to fish communities exists periodically in the upper Serpent River from the interaction of ammonia and pH, it is recommended that a feasibility study into effluent pH control be initiated. This study should determine the effect of effluent pH maintenance in the 6.5 to 7.5 range, recognizing the implications to downstream ammonia oxidation and the mobilization of metals from tailings areas. A study to define the cause of elevated river pH values during the winter months should also be initiated.