An airborne remote sensing study of thermal discharges to Lake Erie and the Detroit and St. Clair Rivers was conducted on 9 July 1973. The study area encompassed the southern shore of Lake Erie from about 5 km (3 mi) east of Ashtabula, Ohio, to Toledo (Maumee Bay), Ohio, and the western shore of Lake Erie from Toledo to the mouth of the Detroit River. The western shores of the Detroit and St. Clair Rivers were also included in the study area. Thermal infrared imagery of the entire study area was obtained using infrared line scanners mounted in high performance reconnaissance aircraft. Ground measurements of water temperatures were made at most of the power plants. This imagery and the ground truth water temperature data were used to characterize the observed thermal fields or plumes.