The problem of the pollution of the rivers and estuaries of this nation and the world is now receiving considerable attention, and rightly so. Many rivers are so grossly polluted that there is scum on the surface and the odor of methane and hydrogen sulfide is noticeable. Consequently, there is a danger to health. For example, part of the Hudson River in New York is so foul that only eels can live in it. The lower Mississippi River is full of fish that have died. Through a great effort over a long period of time, the sewage load on the Potomac River has been reduced. The river has improved greatly and the more desirable species of fish are beginning to return...