The water is sickly green and smells like a sewage plant. Paper wrappers that once held candy and fast food float lazily by on an oil slick, along with a half-submerged tire. And those are only some of the more visible signs of the sickness that afflicts Washington, D.C.’s Anacostia River—once a great waterway plied by tall ships, now a national disgrace.

The Anacostia resembles many other abused rivers around the world. For years people have allowed their waterways to become repositories for sewage, organic and inorganic chemicals, industrial waste, even radioactive and infectious materials. Nitrates, cadmium, mercury, arsenic, and lead combine in a poisonous stew, much of which can find its way into human bloodstreams when we eat fish from a polluted river or drink water that has not been adequately treated.

Oil spills from supertankers and offshore drilling operations threaten the ocean environment. But the major source of marine pollution is runoff from urban, suburban, and agricultural land. Lakes and coastal areas are vulnerable to excessive plant growth, called eutrophication, caused by artificial enrichment from chemical fertilizers and other nutrients. A result: the destruction of habitat for marine animals.