As a contribution to the systematic evaluation of sources of selected trace organics discharged into the St. Clair River in Sarnia, municipal sources, such as urban runoff, drainage ditch flow and wastewater treatment plant effluent, were evaluated. The sampling of these sources indicated the presence of trace organics at fairly low levels. The treated effluent conveyed the highest loadings of perchloroethylene (560 kg/yr) and carbon tetrachloride (4 kg/yr). The drainage ditch receiving some industrial discharges conveyed the highest loadings of hexachlorobutadiene (9 kg/yr) and hexachloroethane (2 kg/yr). The annual loadings of pentachlorobenzene, hexachlorobenzene and octachlorostyrene were smaller than 0.1 kg/yr. The loadings from municipal sources were found insignificant in comparison to those from industrial sources.