Opinion of the Court
For more than a half century, the agencies responsible for enforcing the Act have wrestled with the problem and adopted varying interpretations. On three prior occasions, this Court has tried to clarify the meaning of “the waters of the United States.” But the problem persists. When we last addressed the question 17 years ago, we were unable to agree on an opinion of the Court.[1] Today, we return to the problem and attempt to identify with greater clarity what the Act means by “the waters of the United States.”
I
A
For most of this Nation’s history, the regulation of water pollution was left almost entirely to the States and their subdivisions. The common law permitted aggrieved parties to bring nuisance suits against polluters. But as industrial production and population growth increased the quantity and toxicity of pollution, States gradually shifted to enforcement by regulatory agencies.[2] Conversely, federal regulation was largely limited to ensuring that “traditional navigable waters”—that is, interstate waters that were either navigable in fact and used in commerce or readily susceptible of being used in this way—remained free of impediments. See, e.g., Rivers and Harbors Act of 1899, 30 Stat. 1151; see also United States v. Appalachian Elec. Power Co., 311 U. S. 377, 406–407 (1940); The Daniel Ball, 10 Wall. 557, 563 (1871).
Congress’s early efforts at directly regulating water pollution were tepid. Although the Federal Water Pollution Control Act of 1948 allowed federal officials to seek judicial abatement of pollution in interstate waters, it imposed high
