DDD, DDE and ametryn were the most frequently detected pesticides in sediment in the St. Lucie River Watershed (SLR) and Everglades Agricultural Area (EAA). Concentrations of organochlorine compounds typically exceeded NOAA (SQuiRTs) TELs for freshwater sediment. Microtox BSPT EC50s from sediments in the SLR and EAA were lower than other sediment samples and reference controls. Single-species 10-day toxicity tests with Hyalella azteca and Chironomus tentans and whole sediment sample exposures from the SLR and EAA showed no effects on survival or growth of both species. However, in 28-day tests with H. azteca, survival was reduced at two sites compared to a reference control and a third sampling site. There were no correlations between contaminant concentrations, EC50s and toxicity test results.