(agriculture and silviculture) can cause nonpoint pollution. At first, municipal and industrial wastes simply drained into the nearest watercourse. Later, as populations grew and there were outbreaks of waterborne disease, waste was collected in sewers and diverted away from water intakes. In Chicago, for example (Appendix A), waste was diverted away from Lake Michigan and into the Illinois River, starting on a large scale in 1900. Eventually the assimilative capacity for waste of even the largest rivers was exceeded, and waste treatment plants had to be constructed. Substantial federal assistance for sewage plant construction and upgrading was provided by the Federal Water Pollution Control Act of 1972, and by subsequent legislation, including the landmark Clean Water Act of 1977.

The approach to restoring water quality was to develop criteria for various uses of water and then design waste treatment plants that would achieve effluent standards that in turn would protect or restore the beneficial uses of the stream or river, including fish and wildlife production and use for public water supply. In general, this approach has worked to a substantial degree for conventional pollutants, including oxygen-demanding organic waste, as indicated in the examples of the Illinois and Merrimack rivers, the biennial water quality reports issued by the states under requirements of Section 305 (b) of the Clean Water Act (e.g., Illinois EPA, 1990; ORSANCO, 1990) and national water quality summaries (CEQ, 1989; Smith et al., 1987). However, point and nonpoint discharges of toxicants remain a problem; and a legacy of pollutants, including toxicants, remains in sediments and can enter food chains. For example, public health advisories against consumption of certain nonsport fish in the Ohio River were issued by Pennsylvania, Ohio, West Virginia, and Kentucky in 1987 and 1988 because of high levels of chlordane or polychlorinated biphenyls (PCBs; ORSANCO, 1990; see also Merrimack River and Willamette River case studies, Appendix A).

River-riparian systems are products of how their drainages are covered (vegetation type) and how the land is used (grazed, cropped, or urbanized). Over the past 30 years (1960s through 1980s), major land use categories have changed very little (Flather and Hoekstra, 1989). There has been a slight reduction in rangeland and forest (5 percent each) and a 3 percent increase in cropland. There are regional differences: in the Southeast, forest land has increased substantially. Urban land increased 88 percent, from approximately 25 million acres in 1960 to 47 million acres in 1980 (Flather and Hoekstra,