Technical Abstract: Three oxbow lakes in northwestern Mississippi, USA, an area of intensive agriculture, were assessed for biological impairment from historic and current-use pesticide contamination using the amphipod, Hyalella azteca. Aqueous and sediment samples from three sites in each lake were collected from Deep Hollow, Beasley, and Thighman Lakes from September 2000 to February 2001. Samples were analyzed for 17 historic and current-use pesticides and selected metabolites. Ten-day H. azteca survival and growth (as length and dry weight) were measured to determine the degree of biological impairment. Mean number of detectable pesticides in water from Deep Hollow, Beasley and Thighman Lakes were 9, 11, and 16, respectively. Mean number of detectable pesticides in lake sediments was 16, 16, and 15, respectively. Bioassay results indicated no observable survival effects on H. azteca exposed to water or sediment from any lake examined and no growth impairment in animals exposed to lake sediments. However, growth was significantly impaired in aqueous exposures from Deep Hollow Lake (2 sites) and Beasley Lake (1 site). Relationships between growth impairment (length) and cyanazine, methyl parathion,''-cyhalothrin, chlorfenapyr, and pp' DDE aqueous concentrations in Deep Hollow Lake as well as trifluralin, atrazine, and methyl parathion in Beasley Lake were observed. Although pesticide frequency and concentrations were typically greater in sediment than water, bioassay results indicated decreased availability of these pesticides in sediment due to the presence of clay and organic carbon. Growth impairment observed in aqueous exposures was due to the complex interaction of pesticide mixtures that were present.