One of Aesop's fables tells of a wolf and a lamb who were drinking from the same stream. The wolf snarled at the lamb that it was muddying his drinking water, and that as punishment it would be eaten. "But," the lamb protested, "I can't be muddying your water, I'm downstream from you." The lamb was promptly eaten as a punishment for insolence.

Though told with a different moral in mind, the story illustrates a problem that has created discord since antiquity: users of rivers are notoriously unconcerned with the state of the water reaching their downstream neighbors. In the United States, the issue has been the subject of frequent controversy between the states. In 1965, Congress passed the Water Quality Act, under which states were to prepare implementation plans for improving water quality and submit them to federal authorities for approval. This proved unsatisfactory, however, and in the Federal Water Pollution Control Act Amendments of 1972 (FWPCA), Congress shifted the responsibility for establishing water quality criteria from state officials to the EPA Administrator, whom may impose them on the states. Issued recently in the form of guidelines, these criteria must be given a mixed review.