Streambed-sediment and fish-tissue samples were collected at eight sites in the Great and Little Miami Basins as part of the U.S. Geological Survey's National Water Quality Assessment Program. The samples were analyzed for trace elements and synthetic organic compounds, including organochlorine insecticides, polychlorinated biphenyls (PCBs), and semivolatile compounds (SVOCs). Data from state-agency investigations within the study unit (more than 200 sites) were incorporated to gain a broader perspective of the occurrence and distribution of contaminants in the study unit. All data were compared to streambed-sediment-quality guidelines and fish-tissue guidelines to identify elevated contaminant concentrations. Guideline exceedances were plotted on distribution maps to identify areas in the study unit that may be of potential concern for wildlife health.

Several trace elements were detected in both sediment and fish-tissue samples. In sediment, lead and zinc were most frequently detected at levels that may have adverse effects on aquatic organisms. Generally, only one of the trace elements analyzed for per site exceeded concentrations above which adverse biological effects are frequently anticipated.

Organochlorine insecticides were infrequently detected in sediment or fish tissue throughout the study unit. More organochlorine insecticides were detected in fish tissues than in sediment; however, more guidelines were exceeded in sediment. No distinct geographic overlap between sediment and fish-tissue sites was evident with respect to elevated organochlorine insecticide concentrations. Sediment-quality guideline exceedances were generally widespread throughout the study unit, whereas fish-tissue guidelines were exceeded only on the Mad River.

PCBs were detected more often in fish tissue than in sediment throughout the study unit. Elevated PCB concentrations in fish tissue were common and widespread. No distinct geographic overlap of PCB exceedances was evident between sediment and fish-tissue sites.

In sediments, elevated concentrations were detected most often for SVOCs, particularly for polycyclic aromatic hydrocarbons (PAHs). Areas where SVOC guidelines were frequently exceeded include the Great Miami River main stem from Dayton to south of Hamilton, and the Upper Little Miami River Basin in Greene County.

Overall, a higher frequency of trace-element detections in fish tissue and sediment trace-element guideline exceedances was found in the Great Miami River Basin than in the Little Miami River Basin. Organochlorine insecticide guidelines for fish tissue and sediment, as well as PCB and SVOC guidelines for sediment also were exceeded more frequently in the Great Miami River Basin. PCB guideline exceedances for fish tissue were found more often in the Little Miami River Basin.