An interdisciplinary study was made on the terrestrial and aquatic effects of two organo-toxicants, Phorate and Carbaryl, as applied on experimental watersheds in Southern Indiana. Studied were the physio-chemcial properties of the soil constituents on the sorption reactions of the toxic substances; bacterial degradation of the pesticides in the reservoirs, terrestrial and aquatic indicator organisms which denoted the presence or effect of the substances, and feasible methods for removal of the substance once entered into the water system. The amount of pesticide lost from an application site into the water system was dependent on the occurrence of runoff-producing storms shortly after application. Bacteria were found which could break the ring structure of the carbaryl; however, data concerning the role of microorganisms in the elimination of organo-toxicants from surface water were variable.