Pollution is one of the American public's greatest environmental concerns. Like the proverbial "canary in the coal mine," fish and wildlife often signal pollution problems that ultimately affect people and their quality of life. National Wildlife Refuges are affected by a wide range of contaminants including not only water and air pollution, but invasive plant and animal species, aquatic nuisance species, feral animals, oil spills, pesticides and the consequences of urbanization and agricultural runoff. The U.S. Fish and Wildlife Service is the main federal agency dedicated to protecting wildlife and their habitat from the harmful effects of such contaminants.