The impact of saline waters upon freshwater biota, having special reference to the AOSERP study area, is reviewed. Available information on water quality in the AOSERP study area indicates that: the natural regional surface water quality does not appear to have any toxic effects, and chloride concentrations of groundwaters are quite variable although those associated with mine depressurization are apparently low to moderate. The effects of saline waters in general on major groups of organisms including aquatic plants, aquatic invertebrates, fish birds and mammals are discussed. Toxicity summaries for individual ions are presented. The report also contains an extensive bibliography of scientific references pertaining to the impact of saline waters upon freshwater biota.