High-altitude photography provides an effective method of monitoring the spatial extent of turbidity plumes in Lake Ontario. Large plumes generated by the Niagara, Genesee, and Oswego Rivers are identifiable on photographs obtained from about 60,000 feet above the lake on July 6, 1970, October 19, 1970, and May 29, 1971. The Niagara plume, covering as much as 43 sq mi of the lake's surface, is the largest turbidity feature. The configuration of the plumes is a function of river discharge, level of turbidity, and wind speed and direction.