Reported are studies on: (1) the half-life of the insecticide, methoxychlor, in various aquatic enironments; (2) acute bioassays on Taeniopteryx nivalis, Chironomus tentans and Stenonema candidum; (3) acute and chronic experiments with two species of fish, the fathead minnow (Pimephalis promelas) and the yellow perch (Perca flavescens). The breakdown of methoxychlor was studied in water from three sources: (1) distilled water at pH 7 and pH 9; (2) water from the city of Ann Arbor and (3) water from Kock Warner Creek at the Saline Fisheries Research Station, utilizing the experimental streams. The breakdown of methoxychlor in water was dependent upon microbial degradation. Half-lives under conditions where hydrolysis was the primary mode of breakdown were calculated to be approximately 200 days, whereas in experiments where flora and fauna were present, ranged from 2-7 days. (Author)