Except for the acid parts of the North Branch, the upper Basin's waters in most places, most of the time, can still serve the "practical" purposes to which they are put--irrigation, industrial uses, municipal supply after purification, and even the absorption and digestion of effluents from adequate, well-run treatment plants. Most of the streams are usually good to look at, especially in conjunction with the superb rural landscapes against backgrounds of wooded mountains that are characteristic. They furnish much pleasure to fishermen, hunters, boatmen, swimmers, picnickers, and other folk, though in some places it is an open question, as we have seen, whether or not contact with the water is prudent. And almost everywhere, aging locals can recall a time when their stream was a happier amenity than now--when it held more fish, ran clearer over stones and gravel not coated with weeds and green slime, did not have the smell it presently emanates, was colder and more copious.... Their nostalgia probably does not play them false, even though conditions in many places are better now than in the intermediate past, after modern times had settled in, but before INCOPOT and the Soil Conservation Service and such influences had begun to push for reform of the casual, anciently human ways of doing things in which present human populations can no longer afford to indulge themselves. Some of the gains that have been made are being cancelled out by growth and new types of pollution, however, and in general the flowing Potomac river system is teetering at the brink of bad trouble. It needs help. If the flowing upper Potomac had any lingering oxygen deficiency in its lower stretches--though it seems usually not to--it would tend to rectify the lack in its turbulent eighteen-miles descent across the Fall Line, a superb natural "treatment plant." Normally it arrives at Washington charged with oxygen, but does bring down with it the part of its nutrient load that has not fertilized upstream weeds and algae, periodic waves of bacterial concentration, and a great deal of debris and silt in season. In the broadening, slowing upper estuary, its sluggish currents confused by the twice-daily surge and ebb of tides, these materials from above are stirred in with an array of specifically metropolitan pollutants--with more silt off of the outraged urban watershed, with junk and debris of a thousand sorts, with decaying substances and bacteria from many sources, and with vast new quantities of nitrogen and phosphorus. The consequence is a weighty and sometimes spectacular pollution problem directly adjacent to the proud national capital. It is at its vivid and aromatic worst in summer, when the most Americans come there fondly to view the city and the Potomac, and when locals who want to boat and fish and swim and do the other things one does on water would make most use of the river--indeed, do make use of it in spite of everything.