In civilized parts of the modern world, however, there are now so many people generating so many wastes of one kind and another, which often enter the streams at concentrated points, that the streams can no longer digest them without help. Too often, in the face of uncontrolled human increase and expansion, that help has either been denied them or has been weak and perfunctory. The result is plain enough now in the sorry mess of sick or dead or dying waters that we Americans have on our hands, the heritage of having kept on taking them for granted long after we had bred ourselves out of the right to do so. As civilized rivers go, the Potomac is rather lucky. It is polluted, but many parts of it are not nearly as dirty as people are sometimes led into believing by a look at the summertime estuary at Washington. The fabled and scenic German Rhine, for instance, is much more degraded in its main flowing reaches than is the Potomac, and so are a majority of the other rivers in the northeastern United States and many elsewhere in the country. Industrialization on the Potomac and its tributaries has been spotty so far, and there are no really big clusters of population in the upper parts of the Basin. Furthermore, pollution here has already been given quite a lot of dedicated and expert attention and some rectification. Thus anyone who travels up and down the river and its tributaries finds many miles of pleasant flowing streams capable of sustaining fish and the other things that are supposed to live in and around water, and fit to soothe frayed nerves. He will find a lot of grubby and unsoothing stretches too, extensive in places, and even in the pleasant streams troubles exist that are invisible to the eye. There is little to be complacent about, for threats are multiplying rather than fading, and some parts of the Potomac river system already need more than help; they need resurrection. [Illustration] The Basin has several standard sorts of pollution, often found in one combination or another. Chemical contamination occurs along the North Branch, in areas where pesticides and other economic poisons get into the stream system, and in spots and stretches where specific industrial wastes create local problems. There is much and widespread pollution through organic wastes--often sewage solids, but not always--whose breakdown by natural processes may demand so much oxygen that a stream has little or none left over to maintain aquatic life and "stay alive."