Airborne remote sensing studies of five areas in the Pacific Northwest states of Washington, Oregon and Idaho (Puget Sound, Wash.; Grays Harbor, Wash.; Willamette River, Oreg.; Coeur D'Alene Lake, Idaho; and the Snake and Salmon Rivers, Idaho) were conducted in April and July 1973. Aircraft sensors were selected to record the presence and characteristics of municipal and industrial wastewater discharges. The location and characteristics of detected discharges were compared with those of known discharges reported in Refuse Act Permit Program (RAPP) and National Pollutant Discharge Elimination System (NPDES) permit applications. Discharges from unknown sources that may have originated from nonfilers, and apparent additional or changed discharges at sources filing for permits were identified. The color, dispersion pattern and size of visible plumes for the observed discharges were documented. Color illustrations reproduced in black and white.