One partial success story of the Clean Water Act is the Potomac River, a 462-km (287-mile) water course that begins in West Virginia and flows into the Chesapeake Bay. Pollution episodes in the Potomac date back as early as the 1840s, when sewers first conveyed human wastes to the river from Washington, D.C. According to Civil War–era reports, President Lincoln frequently left the White House to escape odors emanating from the Potomac (Uman, 1994).

Pollution in the river continued to worsen until, in 1934, the federal government appropriated funds to build the Blue Plains sewage treatment plant to remove settleable solids before the sewage entered the river. The plant's capacity was soon exceeded, however. As a result, discharges of raw sewage became increasingly common, and the river continued to deteriorate. In 1969, participants at a Washington, D.C., conference called the Potomac River "a severe threat to anyone who comes in contact with it" (Adler and Finkelstein, 1993). By 1970, the pollutant loading to the river was higher than it had been in 1932 (Uman, 1994). Algal mats choked a 50-mile stretch of the river downstream from Washington in late summer. Fishing and swimming were prohibited.

Following passage of the Clean Water Act, the government spent $1.6 billion to upgrade the Blue Plains plant and in 1980 spent an additional $500 million to add advanced treatment systems. Recreational boating is now possible on the river. Bottom vegetation and bass have returned after a long absence (Uman, 1994).

Despite these notable improvements, swimming in and consuming fish from portions of the river remain health risks (Interstate Commission on the Potomac River Basin, 1994). Contaminants such as chlordane, polychlorinated biphenyls, and heavy metals remain. In addition, the river is subject to bacterial contamination from discharges of raw sewage when major storms overload Blue Plains and other local sewage treatment plants. Thus, although the quality of the Potomac has improved substantially, it still does not meet the "fishable and swimmable" goal of the Clean Water Act.

billion in revenues (including freshwater and saltwater harvests) in 1990 (Adler and Finkelstein, 1993). According to the EPA (1994), 1,279 fish consumption advisories—warning consumers and fishermen to limit intake of certain fish because of contamination—were in effect in 47 states in 1993; contaminant levels in fish tissues can be more than a million times those in surrounding water because of the tendency of contaminants to concentrate in species at higher levels of the aquatic food web.

The need to provide more advanced levels of treatment for degraded sources of drinking water also has significant costs. For example, New York City may eventually be required to filter its drinking water because

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