166
Opinion of the Court
the CWA to cover nonnavigable, isolated, intrastate waters based upon the presence of migratory birds and, in the alternative, that Congress lacked the power under the Commerce Clause to grant such regulatory jurisdiction.
The Court of Appeals began its analysis with the constitutional question, holding that Congress has the authority to regulate such waters based upon "the cumulative impact doctrine, under which a single activity that itself has no discernible effect on interstate commerce may still be regulated if the aggregate effect of that class of activity has a substantial impact on interstate commerce." 191 F. 3d 845, 850 (CA7 1999). The aggregate effect of the "destruction of the natural habitat of migratory birds" on interstate commerce, the court held, was substantial because each year millions of Americans cross state lines and spend over a billion dollars to hunt and observe migratory birds.2 Ibid. The Court of Appeals then turned to the regulatory question. The court held that the CWA reaches as many waters as the Commerce Clause allows and, given its earlier Commerce Clause ruling, it therefore followed that respondents' "Migratory Bird Rule" was a reasonable interpretation of the Act. See id., at 851-852.
We granted certiorari, 529 U. S. 1129 (2000), and now reverse.
Congress passed the CWA for the stated purpose of "restor[ing] and maintain[ing] the chemical, physical, and biological integrity of the Nation's waters." 33 U. S. C. § 1251(a). In so doing, Congress chose to "recognize, preserve, and protect the primary responsibilities and rights of
2 Relying upon its earlier decision in Hoffman Homes, Inc. v. EPA, 999 F. 2d 256 (CA7 1993), and a report from the United States Census Bureau, the Court of Appeals found that in 1996 approximately 3.1 million Americans spent $1.3 billion to hunt migratory birds (with 11 percent crossing state lines to do so) as another 17.7 million Americans observed migratory birds (with 9.5 million traveling for the purpose of observing shorebirds). See 191 F. 3d, at 850.
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