Another way in which the character of rivers is drastically altered is by cutting off interactions with the riparian zone and floodplains. This may be done directly, by channelization and leveeing (Kissimmee, Illinois, and Mississippi rivers), and indirectly, by regulating the flood regime (navigation dams on the Mississippi). According to the American Rivers Conservation Council (Echeverria et al., 1989), of approximately 3.2 million miles of rivers in the United States, 2.9 million miles remain undammed, while 600,000 miles of river are dammed. The committee could not find a recent national assessment of the number of stream and river miles affected by channelization or leveeing, but the total is probably much greater than the number of miles of river dammed. In the Illinois River, for example, half the floodplain has been leveed (Bellrose et al., 1983), and most of the Lower Mississippi River is leveed (Fremling et al., 1989). Although water resource agencies track their own development projects, the only nationwide inventory of rivers and streams was conducted in the 1970s (U.S. DOI, 1982) in response to passage of the Wild and Scenic Rivers Act of 1968 (P.L. 90-542). The purpose of the inventory was to identify those rivers worthy of the designation wild and scenic, and so narrow were the criteria that less than 2 percent of total river mileage qualified for inclusion on the list. Therefore, there remains a need for a comprehensive up-to-date nationwide assessment of rivers, comparable to the National Wetland Inventory (Tiner, 1984). It would be useful to know how many miles of free-flowing, unchannelized rivers remain in the United States, where these reaches are located, and what the current trends (net gains or losses) are.
Progress has been made in controlling conventional pollution (sewage and other organic wastes) from point sources. In many parts of the United States, water quality has been maintained or restored since the institution of the clean water acts, starting around 1965, although problems remain in some reaches (CEQ, 1989; ORSANCO, 1990). In some cases (e.g., the Willamette and Illinois rivers), water quality in certain critical reaches is maintained only by dilution, and fish and other aquatic organisms are affected by a legacy of toxic substances in sediment deposits. Also, national water quality assessments are based on lake or channel sampling that does not include floodplain pools and backwaters; so the status of these important nursery areas for fish and wildlife is poorly documented.
Since the passage of the Federal Surface Mining Control and Reclamation Act of 1977 (P.L. 95-87), mining companies have been required to restore both land and water affected by mining and acid mine drainage, in most cases to their premining uses. A federal tax on coal provides funds to restore lands abandoned before the act