This paper presents the seasonal and annual variations of the physical parameters, nutrients and major ions in the Niagara River for a period of eleven years, 1977–87. The discharge during this period was found to be steadily increasing and as a consequence the specific conductance was decreasing due to the higher dilution effect, as well as the lower concentrations of chloride and sodium. High concentrations of total phosphorus during the winter months corresponded with high turbidity. In addition, a steady decrease in total phosphorus concentrations was observed until 1984, while during the rest of the period concentrations were increasing. Nitrate nitrogen concentrations were found to be steadily increasing during the entire period except for 1987. Seasonal cycles of specific conductance, calcium, alkalinity, magnesium, and sulphate all showed decreases in April, May and June, during the high discharge period. Both chloride and sodium concentrations have decreased substantially during the 1977–85 period, the result of upstream industrial input decreases, but concentrations since then have levelled out.