Results from the National Lake Fish Tissue Study indicate that mercury, PCBs, and dioxins and furans are widely distributed in lakes and reservoirs in the lower 48 states. These waterbodies occur in a variety of landscapes, and they can receive contaminants from several sources, including direct discharges in the water, air deposition and agricultural or urban runoff. Monitoring fish contamination in lakes and reservoirs is a critical activity for protecting human and ecosystem health because lakes and reservoirs provide important sports fisheries and other recreational opportunities. Lake ecosystems also provide critical habitat for aquatic species, and they support wildlife populations that depend on aquatic species for food. This book is a study of contaminants found in fish and their environmental impact.