Despite tremendous progress, 40 percent of the nation's waterways assessed by states are still unsafe for fishing and swimming. Pollution from factories and sewage treatment plants, soil erosion, and wetland losses have been dramatically reduced. But runoff from city streets, rural areas, and other sources continues to degrade the environment and puts drinking water at risk. Fish in many waters still contain dangerous levels of mercury, polychlorinated biphenyls (PCBs), and other toxic contaminants.