U.S. Geological Survey U.S. Geological Survey As part of the National Water-Quality Assessment (NAWQA) Program, tissue and whole-body samples of aquatic biota were analyzed for organic and trace-element contaminants. Five species of fish and four species of macroinvertebrates were collected from 13 sites in 1992. An additional 10 sites were sampled for tissue in 1993. Patterns of contaminant concentrations among aquatic species and bed sediment were evaluated as measures of contaminant occurrence and distribution. Comparisons of concentrations of tissue organic contaminants between fish and the Asiatic Clam (Corbicula fluminea) revealed that sculpins (Cottus spp.) contained organic contaminants at levels higher than in Corbicula. In part, higher lipid levels in sculpins may have accounted for the comparative increase in tissue organic contaminants. In contrast, trace-elements were generally higher in the Asiatic clam than in the sculpins. Overall, trace-element concentrations in aquatic biota and bed sediment varied similarly in magnitude among sites, although concentration levels were often greater in the sediment samples. Preliminary results assessing contaminant occurrence from both point- and nonpoint-source pollution are presented.