531 U.S. 159 (2001)

SOLID WASTE AGENCY OF NORTHERN COOK COUNTY
v.
UNITED STATES ARMY CORPS OF ENGINEERS et al.

No. 99-1178.

United States Supreme Court.

Argued October 31, 2000. Decided January 9, 2001. CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE SEVENTH CIRCUIT

*160 *161 Rehnquist, C. J., delivered the opinion of the Court, in which O'Connor, Scalia, Kennedy, and Thomas, JJ., joined. Stevens, J., filed a dissenting opinion, in which Souter, Ginsburg, and Breyer, JJ., joined, post, p. 174.

Timothy S. Bishop argued the cause for petitioner. With him on the briefs were Kaspar J. Stoffelmayr, Sharon Swingle, and George J. Mannina, Jr.

Deputy Solicitor General Wallace argued the cause for respondents. With him on the brief for the federal respondents were Solicitor General Waxman, Assistant Attorney General Schiffer, Malcolm L. Stewart, and John A. Bryson. Myron M. Cherry filed a brief for respondents Village of Bartlett et al.^[*]

*162 Chief Justice Rehnquist delivered the opinion of the Court.

Section 404(a) of the Clean Water Act (CWA or Act), 86 Stat. 884, as amended, 33 U. S. C. § 1344(a), regulates the discharge of dredged or fill material into "navigable waters." The United States Army Corps of Engineers (Corps) has interpreted § 404(a) to confer federal authority over an abandoned sand and gravel pit in northern Illinois which provides habitat for migratory birds. We are asked to decide whether the provisions of § 404(a) may be fairly extended to these waters, and, if so, whether Congress could exercise such authority consistent with the Commerce Clause, U. S. Const., Art. I, § 8, cl. 3. We answer the first question in the negative and therefore do not reach the second.

Petitioner, the Solid Waste Agency of Northern Cook County (SWANCC), is a consortium of 23 suburban Chicago *163 cities and villages that united in an effort to locate and develop a disposal site for baled nonhazardous solid waste. The Chicago Gravel Company informed the municipalities of the availability of a 533-acre parcel, bestriding the Illinois counties Cook and Kane, which had been the site of a sand and gravel pit mining operation for three decades up until about 1960. Long since abandoned, the old mining site eventually gave way to a successional stage forest, with its remnant excavation trenches evolving into a scattering of permanent and seasonal ponds of varying size (from under one-tenth of an acre to several acres) and depth (from several inches to several feet).

The municipalities decided to purchase the site for disposal of their baled nonhazardous solid waste. By law, SWANCC was required to file for various permits from Cook County and the State of Illinois before it could begin operation of its bale fill project. In addition, because the operation called for the filling of some of the permanent and seasonal ponds, SWANCC contacted federal respondents (hereinafter respondents), including the Corps, to determine if a federal landfill permit was required under § 404(a) of the CWA, 33 U. S. C. § 1344(a).

Section 404(a) grants the Corps authority to issue permits "for the discharge of dredged or fill material into the navigable waters at specified disposal sites." Ibid. The term "navigable waters" is defined under the Act as "the waters of the United States, including the territorial seas." § 1362(7). The Corps has issued regulations defining the term "waters of the United States" to include

"waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds, the use, degradation or destruction of which could affect interstate or foreign commerce . . . ." 33 CFR § 328.3(a)(3) (1999).

*164 In 1986, in an attempt to "clarify" the reach of its jurisdiction, the Corps stated that § 404(a) extends to in strastate waters:

"a. Which are or would be used as habitat by birds protected by Migratory Bird Treaties; or

"b. Which are or would be used as habitat by other migratory birds which cross state lines; or

"c. Which are or would be used as habitat for endangered species; or

"d. Used to irrigate crops sold in interstate commerce." 51 Fed. Reg. 41217.

This last promulgation has been dubbed the "Migratory Bird Rule."^[1]

The Corps initially concluded that it had no jurisdiction over the site because it contained no "wetlands," or areas which support "vegetation typically adapted for life in saturated soil conditions," 33 CFR § 328.3(b) (1999). However, after the Illinois Nature Preserves Commission informed the Corps that a number of migratory bird species had been observed at the site, the Corps reconsidered and ultimately asserted jurisdiction over the balefill site pursuant to subpart (b) of the "Migratory Bird Rule." The Corps found that approximately 121 bird species had been observed at the site, including several known to depend upon aquatic environments for a significant portion of their life requirements. Thus, on November 16, 1987, the Corps formally "determined that the seasonally ponded, abandoned gravel mining depressions located on the project site, while not wetlands, did qualify as `waters of the United States' . . . based upon the following criteria: (1) the proposed site had been abandoned as a gravel mining operation; (2) the water areas and spoil piles had developed a natural character; and (3) the water areas *165 are used as habitat by migratory bird [sic] which cross state lines." U. S. Army Corps of Engineers, Chicago District, Dept. of Army Permit Evaluation and Decision Document, Lodging of Petitioner, Tab No. 1, p. 6.

During the application process, SWANCC made several proposals to mitigate the likely displacement of the migratory birds and to preserve a great blue heron rookery located on the site. Its balefill project ultimately received the necessary local and state approval. By 1993, SWANCC had received a special use planned development permit from the Cook County Board of Appeals, a landfill development permit from the Illinois Environmental Protection Agency, and approval from the Illinois Department of Conservation.

Despite SWANCC's securing the required water quality certification from the Illinois Environmental Protection Agency, the Corps refused to issue a § 404(a) permit. The Corps found that SWANCC had not established that its proposal was the "least environmentally damaging, most practicable alternative" for disposal of nonhazardous solid waste; that SWANCC's failure to set aside sufficient funds to remediate leaks posed an "unacceptable risk to the public's drinking water supply"; and that the impact of the project upon area-sensitive species was "unmitigatable since a landfill surface cannot be redeveloped into a forested habitat." Id., at 87.

Petitioner filed suit under the Administrative Procedure Act, 5 U. S. C. § 701 et seq., in the Northern District of Illinois challenging both the Corps' jurisdiction over the site and the merits of its denial of the § 404(a) permit. The District Court granted summary judgment to respondents on the jurisdictional issue, and petitioner abandoned its challenge to the Corps' permit decision. On appeal to the Court of Appeals for the Seventh Circuit, petitioner renewed its attack on respondents' use of the "Migratory Bird Rule" to assert jurisdiction over the site. Petitioner argued that respondents had exceeded their statutory authority in interpreting *166 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 *167 States to prevent, reduce, and eliminate pollution, to plan the development and use (including restoration, preservation, and enhancement) of land and water resources, and to consult with the Administrator in the exercise of his authority under this chapter." § 1251(b). Relevant here, § 404(a) authorizes respondents to regulate the discharge of fill material into "navigable waters," 33 U. S. C. § 1344(a), which the statute defines as "the waters of the United States, including the territorial seas," § 1362(7). Respondents have interpreted these words to cover the abandoned gravel pit at issue here because it is used as habitat for migratory birds. We conclude that the "Migratory Bird Rule" is not fairly supported by the CWA.

This is not the first time we have been called upon to evaluate the meaning of § 404(a). In United States v. Riverside Bayview Homes, Inc., 474 U. S. 121 (1985), we held that the Corps had § 404(a) jurisdiction over wetlands that actually abutted on a navigable waterway. In so doing, we noted that the term "navigable" is of "limited import" and that Congress evidenced its intent to "regulate at least some waters that would not be deemed `navigable' under the classical understanding of that term." Id., at 133. But our holding was based in large measure upon Congress' unequivocal acquiescence to, and approval of, the Corps' regulations interpreting the CWA to cover wetlands adjacent to navigable waters. See id., at 135-139. We found that Congress' concern for the protection of water quality and aquatic ecosystems indicated its intent to regulate wetlands "inseparably bound up with the `waters' of the United States." Id., at 134.

It was the significant nexus between the wetlands and "navigable waters" that informed our reading of the CWA in Riverside Bayview Homes. Indeed, we did not "express any opinion" on the "question of the authority of the Corps to regulate discharges of fill material into wetlands that are not adjacent to bodies of open water . . . ." Id., at 131-132, *168 n. 8. In order to rule for respondents here, we would have to hold that the jurisdiction of the Corps extends to ponds that are not adjacent to open water. But we conclude that the text of the statute will not allow this.

Indeed, the Corps' original interpretation of the CWA, promulgated two years after its enactment, is inconsistent with that which it espouses here. Its 1974 regulations defined § 404(a)'s "navigable waters" to mean "those waters of the United States which are subject to the ebb and flow of the tide, and/or are presently, or have been in the past, or may be in the future susceptible for use for purposes of interstate or foreign commerce." 33 CFR § 209.120(d)(1). The Corps emphasized that "[i]t is the water body's capability of use by the public for purposes of transportation or commerce which is the determinative factor." § 209.260(e)(1). Respondents put forward no persuasive evidence that the Corps mistook Congress' intent in 1974.^[3]

Respondents next contend that whatever its original aim in 1972, Congress charted a new course five years later when it approved the more expansive definition of "navigable waters" found in the Corps' 1977 regulations. In July 1977, the Corps formally adopted 33 CFR § 323.2(a)(5) (1978), which defined "waters of the United States" to include "isolated wetlands and lakes, intermittent streams, prairie potholes, and other waters that are not part of a tributary system to interstate waters or to navigable waters of the United States, the degradation or destruction of which could affect *169 interstate commerce." Respondents argue that Congress was aware of this more expansive interpretation during its 1977 amendments to the CWA. Specifically, respondents point to a failed House bill, H. R. 3199, that would have defined "navigable waters" as "all waters which are presently used, or are susceptible to use in their natural condition or by reasonable improvement as a means to transport interstate or foreign commerce." 123 Cong. Rec. 10420, 10434 (1977).^[4] They also point to the passage in § 404(g)(1) that authorizes a State to apply to the Environmental Protection Agency for permission "to administer its own individual and general permit program for the discharge of dredged or fill material into the navigable waters (other than those waters which are presently used, or are susceptible to use in their natural condition or by reasonable improvement as a means to transport interstate or foreign commerce . . . , including wetlands adjacent thereto) within its jurisdiction . . . ." 33 U. S. C. § 1344(g)(1). The failure to pass legislation that would have overturned the Corps' 1977 regulations and the extension of jurisdiction in § 404(g) to waters "other than" traditional "navigable waters," respondents submit, indicate that Congress recognized and accepted a broad definition of "navigable waters" that includes nonnavigable, isolated, intrastate waters.

Although we have recognized congressional acquiescence to administrative interpretations of a statute in some situations, we have done so with extreme care.^[5] "[F]ailed legislative *170 proposals are `a particularly dangerous ground on which to rest an interpretation of a prior statute.' " Central Bank of Denver, N. A. v. First Interstate Bank of Denver, N. A., 511 U. S. 164, 187 (1994) (quoting Pension Benefit Guaranty Corporation v. LTV Corp., 496 U. S. 633, 650 (1990)). A bill can be proposed for any number of reasons, and it can be rejected for just as many others. The relationship between the actions and inactions of the 95th Congress and the intent of the 92d Congress in passing § 404(a) is also considerably attenuated. Because "subsequent history is less illuminating than the contemporaneous evidence," Hagen v. Utah, 510 U. S. 399, 420 (1994), respondents face a difficult task in overcoming the plain text and import of § 404(a).

We conclude that respondents have failed to make the necessary showing that the failure of the 1977 House bill demonstrates Congress' acquiescence to the Corps' regulations or the "Migratory Bird Rule," which, of course, did not first appear until 1986. Although respondents cite some legislative history showing Congress' recognition of the Corps' assertion of jurisdiction over "isolated waters,"^[6] as we explained in Riverside Bayview Homes, "[i]n both Chambers, debate on the proposals to narrow the definition of navigable waters centered largely on the issue of wetlands preservation." 474 U. S., at 136. Beyond Congress' desire to regulate *171 wetlands adjacent to "navigable waters," respondents point us to no persuasive evidence that the House bill was proposed in response to the Corps' claim of jurisdiction over nonnavigable, isolated, intrastate waters or that its failure indicated congressional acquiescence to such jurisdiction.

Section 404(g) is equally unenlightening. In Riverside Bayview Homes we recognized that Congress intended the phrase "navigable waters" to include "at least some waters that would not be deemed `navigable' under the classical understanding of that term." Id., at 133. But § 404(g) gives no intimation of what those waters might be; it simply refers to them as "other . . . waters." Respondents conjecture that "other . . . waters" must incorporate the Corps' 1977 regulations, but it is also plausible, as petitioner contends, that Congress simply wanted to include all waters adjacent to "navigable waters," such as nonnavigable tributaries and streams. The exact meaning of § 404(g) is not before us and we express no opinion on it, but for present purposes it is sufficient to say, as we did in Riverside Bayview Homes, that "§ 404(g)(1) does not conclusively determine the construction to be placed on the use of the term `waters' elsewhere in the Act (particularly in § 502(7), which contains the relevant definition of `navigable waters') . . . ." Id., at 138, n. 11.^[7]

We thus decline respondents' invitation to take what they see as the next ineluctable step after Riverside Bayview Homes: holding that isolated ponds, some only seasonal, wholly located within two Illinois counties, fall under § 404(a)'s definition of "navigable waters" because they serve *172 as habitat for migratory birds. As counsel for respondents conceded at oral argument, such a ruling would assume that "the use of the word navigable in the statute . . . does not have any independent significance." Tr. of Oral Arg. 28. We cannot agree that Congress' separate definitional use of the phrase "waters of the United States" constitutes a basis for reading the term "navigable waters" out of the statute. We said in Riverside Bayview Homes that the word "navigable" in the statute was of "limited import," 474 U. S., at 133, and went on to hold that § 404(a) extended to nonnavigable wetlands adjacent to open waters. But it is one thing to give a word limited effect and quite another to give it no effect whatever. The term "navigable" has at least the import of showing us what Congress had in mind as its authority for enacting the CWA: its traditional jurisdiction over waters that were or had been navigable in fact or which could reasonably be so made. See, e. g., United States v. Appalachian Elec. Power Co., 311 U. S. 377, 407-408 (1940).

Respondents—relying upon all of the arguments addressed above—contend that, at the very least, it must be said that Congress did not address the precise question of § 404(a)'s scope with regard to nonnavigable, isolated, intrastate waters, and that, therefore, we should give deference to the "Migratory Bird Rule." See, e. g., Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984). We find § 404(a) to be clear, but even were we to agree with respondents, we would not extend Chevron deference here.

Where an administrative interpretation of a statute invokes the outer limits of Congress' power, we expect a clear indication that Congress intended that result. See Edward J. DeBartolo Corp. v. Florida Gulf Coast Building & Constr. Trades Council, 485 U. S. 568, 575 (1988). This requirement stems from our prudential desire not to needlessly reach constitutional issues and our assumption that Congress does not casually authorize administrative agencies to interpret a *173 statute to push the limit of congressional authority. See ibid. This concern is heightened where the administrative interpretation alters the federal-state framework by permitting federal encroachment upon a traditional state power. See United States v. Bass, 404 U. S. 336, 349 (1971) ("[U]nless Congress conveys its purpose clearly, it will not be deemed to have significantly changed the federal-state balance"). Thus, "where an otherwise acceptable construction of a statute would raise serious constitutional problems, the Court will construe the statute to avoid such problems unless such construction is plainly contrary to the intent of Congress." DeBartolo, supra, at 575.

Twice in the past six years we have reaffirmed the proposition that the grant of authority to Congress under the Commerce Clause, though broad, is not unlimited. See United States v. Morrison, 529 U. S. 598 (2000); United States v. Lopez, 514 U. S. 549 (1995). Respondents argue that the "Migratory Bird Rule" falls within Congress' power to regulate intrastate activities that "substantially affect" interstate commerce. They note that the protection of migratory birds is a "national interest of very nearly the first magnitude," Missouri v. Holland, 252 U. S. 416, 435 (1920), and that, as the Court of Appeals found, millions of people spend over a billion dollars annually on recreational pursuits relating to migratory birds. These arguments raise significant constitutional questions. For example, we would have to evaluate the precise object or activity that, in the aggregate, substantially affects interstate commerce. This is not clear, for although the Corps has claimed jurisdiction over petitioner's land because it contains water areas used as habitat by migratory birds, respondents now, post litem motam, focus upon the fact that the regulated activity is petitioner's municipal landfill, which is "plainly of a commercial nature." Brief for Federal Respondents 43. But this is a far cry, indeed, from the "navigable waters" and "waters of the United States" to which the statute by its terms extends.

*174 These are significant constitutional questions raised by respondents' application of their regulations, and yet we find nothing approaching a clear statement from Congress that it intended § 404(a) to reach an abandoned sand and gravel pit such as we have here. Permitting respondents to claim federal jurisdiction over ponds and mudflats falling within the "Migratory Bird Rule" would result in a significant impingement of the States' traditional and primary power over land and water use. See, e. g., Hess v. Port Authority TransHudson Corporation, 513 U. S. 30, 44 (1994) ("[R]egulation of land use [is] a function traditionally performed by local governments"). Rather than expressing a desire to readjust the federal-state balance in this manner, Congress chose to "recognize, preserve, and protect the primary responsibilities and rights of States . . . to plan the development and use . . . of land and water resources . . . ." 33 U. S. C. § 1251(b). We thus read the statute as written to avoid the significant constitutional and federalism questions raised by respondents' interpretation, and therefore reject the request for administrative deference.^[8]

We hold that 33 CFR § 328.3(a)(3) (1999), as clarified and applied to petitioner's balefill site pursuant to the "Migratory Bird Rule," 51 Fed. Reg. 41217 (1986), exceeds the authority granted to respondents under § 404(a) of the CWA. The judgment of the Court of Appeals for the Seventh Circuit is therefore

Reversed.

Justice Stevens, with whom Justice Souter, Justice Ginsburg, and Justice Breyer join, dissenting.

In 1969, the Cuyahoga River in Cleveland, Ohio, coated with a slick of industrial waste, caught fire. Congress responded *175 to that dramatic event, and to others like it, by enacting the Federal Water Pollution Control Act (FWPCA) Amendments of 1972, 86 Stat. 817, as amended, 33 U. S. C. § 1251 et seq., commonly known as the Clean Water Act (Clean Water Act, CWA, or Act).^[1] The Act proclaimed the ambitious goal of ending water pollution by 1985. § 1251(a). The Court's past interpretations of the CWA have been fully consistent with that goal. Although Congress' vision of zero pollution remains unfulfilled, its pursuit has unquestionably retarded the destruction of the aquatic environment. Our Nation's waters no longer burn. Today, however, the Court takes an unfortunate step that needlessly weakens our principal safeguard against toxic water.

It is fair to characterize the Clean Water Act as "watershed" legislation. The statute endorsed fundamental changes in both the purpose and the scope of federal regulation of the Nation's waters. In § 13 of the Rivers and Harbors Appropriation Act of 1899 (RHA), 30 Stat. 1152, as amended, 33 U. S. C. § 407, Congress had assigned to the Army Corps of Engineers (Corps) the mission of regulating discharges into certain waters in order to protect their use as highways for the transportation of interstate and foreign commerce; the scope of the Corps' jurisdiction under the RHA accordingly extended only to waters that were "navigable." In the CWA, however, Congress broadened the Corps' mission to include the purpose of protecting the quality of our Nation's waters for esthetic, health, recreational, and environmental uses. The scope of its jurisdiction was therefore redefined to encompass all of "the waters of the United States, including the territorial seas." § 1362(7). That definition requires neither actual nor potential navigability.

The Court has previously held that the Corps' broadened jurisdiction under the CWA properly included an 80-acre *176 parcel of low-lying marshy land that was not itself navigable, directly adjacent to navigable water, or even hydrologically connected to navigable water, but which was part of a larger area, characterized by poor drainage, that ultimately abutted a navigable creek. United States v. Riverside Bayview Homes, Inc., 474 U. S. 121 (1985).^[2] Our broad finding in Riverside Bayview that the 1977 Congress had acquiesced in the Corps' understanding of its jurisdiction applies equally to the 410-acre parcel at issue here. Moreover, once Congress crossed the legal watershed that separates navigable streams of commerce from marshes and inland lakes, there is no principled reason for limiting the statute's protection to those waters or wetlands that happen to lie near a navigable stream.

In its decision today, the Court draws a new jurisdictional line, one that invalidates the 1986 migratory bird regulation as well as the Corps' assertion of jurisdiction over all waters *177 except for actually navigable waters, their tributaries, and wetlands adjacent to each. Its holding rests on two equally untenable premises: (1) that when Congress passed the 1972 CWA, it did not intend "to exert anything more than its commerce power over navigation," ante, at 168, n. 3; and (2) that in 1972 Congress drew the boundary defining the Corps' jurisdiction at the odd line on which the Court today settles.

As I shall explain, the text of the 1972 amendments affords no support for the Court's holding, and amendments Congress adopted in 1977 do support the Corps' present interpretation of its mission as extending to so-called "isolated" waters. Indeed, simple common sense cuts against the particular definition of the Corps' jurisdiction favored by the majority.

I

The significance of the FWPCA Amendments of 1972 is illuminated by a reference to the history of federal water regulation, a history that the majority largely ignores. Federal regulation of the Nation's waters began in the 19th century with efforts targeted exclusively at "promot[ing] water transportation and commerce." Kalen, Commerce to Conservation: The Call for a National Water Policy and the Evolution of Federal Jurisdiction Over Wetlands, 69 N. D. L. Rev. 873, 877 (1993). This goal was pursued through the various Rivers and Harbors Acts, the most comprehensive of which was the RHA of 1899.^[3] Section 13 of the 1899 RHA, commonly known as the Refuse Act, prohibited the discharge of "refuse" into any "navigable water" or its tributaries, as well as the deposit of "refuse" on the bank of a navigable water "whereby navigation shall or may be impeded or obstructed" without first obtaining a permit from the Secretary of the Army. 30 Stat. 1152.

*178 During the middle of the 20th century, the goals of federal water regulation began to shift away from an exclusive focus on protecting navigability and toward a concern for preventing environmental degradation. Kalen, 69 N. D. L. Rev., at 877-879, and n. 30. This awakening of interest in the use of federal power to protect the aquatic environment was helped along by efforts to reinterpret § 13 of the RHA in order to apply its permit requirement to industrial discharges into navigable waters, even when such discharges did nothing to impede navigability. See, e. g., United States v. Republic Steel Corp., 362 U. S. 482, 490-491 (1960) (noting that the term "refuse" in § 13 was broad enough to include industrial waste).^[4] Seeds of this nascent concern with pollution control can also be found in the FWPCA, which was first enacted in 1948 and then incrementally expanded in the following years.^[5]

*179 The shift in the focus of federal water regulation from protecting navigability toward environmental protection reached a dramatic climax in 1972, with the passage of the CWA. The Act, which was passed as an amendment to the existing FWPCA, was universally described by its supporters as the first truly comprehensive federal water pollution legislation. The "major purpose" of the CWA was "to establish a comprehensive long-range policy for the elimination of water pollution." S. Rep. No. 92-414, p. 95 (1971), 2 Legislative History of the Water Pollution Control Act Amendments of 1972 (Committee Print compiled for the Senate Committee on Public Works by the Library of Congress), Ser. No. 93-1, p. 1511 (1971) (hereinafter Leg. Hist.) (emphasis added). And "[n]o Congressman's remarks on the legislation were complete without reference to [its] `comprehensive' nature . . . ." Milwaukee v. Illinois, 451 U. S. 304, 318 (1981) (Rehnquist, J.). A House sponsor described the bill as "the most comprehensive and far-reaching water pollution bill we have ever drafted," 1 Leg. Hist. 369 (Rep. Mizell), and Senator Randolph, Chairman of the Committee on Public Works, stated: "It is perhaps the most comprehensive legislation that the Congress of the United States has ever developed in this particular field of the environment." 2 id., at 1269. This Court was therefore undoubtedly correct when it described the 1972 amendments as establishing "a comprehensive program for controlling and abating water pollution." Train v. City of New York, 420 U. S. 35, 37 (1975).

Section 404 of the CWA resembles § 13 of the RHA, but, unlike the earlier statute, the primary purpose of which is the maintenance of navigability, § 404 was principally intended as a pollution control measure. A comparison of the contents of the RHA and the 1972 Act vividly illustrates the fundamental difference between the purposes of the two provisions. The earlier statute contains pages of detailed appropriations for improvements in specific navigation facilities, 30 Stat. 1121-1149, for studies concerning the feasibility *180 of a canal across the Isthmus of Panama, id., at 1150, and for surveys of the advisability of harbor improvements at numerous other locations, id., at 1155-1161. Tellingly, § 13, which broadly prohibits the discharge of refuse into navigable waters, contains an exception for refuse "flowing from streets and sewers . . . in a liquid state." Id., at 1152.

The 1972 Act, in contrast, appropriated large sums of money for research and related programs for water pollution control, 86 Stat. 816-833, and for the construction of water treatment works, id., at 833-844. Strikingly absent from its declaration of "goals and policy" is any reference to avoiding or removing obstructions to navigation. Instead, the principal objective of the Act, as stated by Congress in § 101, was "to restore and maintain the chemical, physical, and biological integrity of the Nation's waters." 33 U. S. C. § 1251. Congress therefore directed federal agencies in § 102 to "develop comprehensive programs for preventing, reducing, or eliminating the pollution of the navigable waters and ground waters and improving the sanitary condition of surface and underground waters." 33 U. S. C. § 1252. The CWA commands federal agencies to give "due regard," not to the interest of unobstructed navigation, but rather to "improvements which are necessary to conserve such waters for the protection and propagation of fish and aquatic life and wildlife [and] recreational purposes." Ibid.

Because of the statute's ambitious and comprehensive goals, it was, of course, necessary to expand its jurisdictional scope. Thus, although Congress opted to carry over the traditional jurisdictional term "navigable waters" from the RHA and prior versions of the FWPCA, it broadened the definition of that term to encompass all "waters of the United States." § 1362(7).^[6] Indeed, the 1972 conferees arrived at the final formulation by specifically deleting the *181 word "navigable" from the definition that had originally appeared in the House version of the Act.^[7] The majority today undoes that deletion.

The Conference Report explained that the definition in § 502(7) was intended to "be given the broadest possible constitutional interpretation." S. Conf. Rep. No. 92-1236, p. 144 (1972), reprinted in 1 Leg. Hist. 327. The Court dismisses this clear assertion of legislative intent with the back of its hand. Ante, at 168, n. 3. The statement, it claims, "signifies that Congress intended to exert [nothing] more than its commerce power over navigation." Ibid.

The majority's reading drains all meaning from the conference amendment. By 1972, Congress' Commerce Clause power over "navigation" had long since been established. The Daniel Ball, 10 Wall. 557 (1871); Gilman v. Philadelphia, 3 Wall. 713 (1866); Gibbons v. Ogden, 9 Wheat. 1 (1824). Why should Congress intend that its assertion of federal jurisdiction be given the "broadest possible constitutional interpretation" if it did not intend to reach beyond the very heartland of its commerce power? The activities regulated by the CWA have nothing to do with Congress' "commerce power over navigation." Indeed, the goals of the 1972 statute have nothing to do with navigation at all.

As we recognized in Riverside Bayview, the interests served by the statute embrace the protection of "`significant natural biological functions, including food chain production, general habitat, and nesting, spawning, rearing and resting sites' " for various species of aquatic wildlife. 474 U. S., at 134-135. For wetlands and "isolated" inland lakes, that interest *182 is equally powerful, regardless of the proximity of the swamp or the water to a navigable stream. Nothing in the text, the stated purposes, or the legislative history of the CWA supports the conclusion that in 1972 Congress contemplated—much less commanded—the odd jurisdictional line that the Court has drawn today.

The majority accuses respondents of reading the term "navigable" out of the statute. Ante, at 172. But that was accomplished by Congress when it deleted the word from the § 502(7) definition. After all, it is the definition that is the appropriate focus of our attention. Babbitt v. Sweet Home Chapter, Communities for Great Ore., 515 U. S. 687, 697-698, n. 10 (1995) (refusing to be guided by the common-law definition of the term "take" when construing that term within the Endangered Species Act of 1973 and looking instead to the meaning of the terms contained in the definition of "take" supplied by the statute). Moreover, a proper understanding of the history of federal water pollution regulation makes clear that—even on respondents' broad reading—the presence of the word "navigable" in the statute is not inexplicable. The term was initially used in the various Rivers and Harbors Acts because (1) at the time those statutes were first enacted, Congress' power over the Nation's waters was viewed as extending only to "water bodies that were deemed `navigable' and therefore suitable for moving goods to or from markets," Power 513; and (2) those statutes had the primary purpose of protecting navigation. Congress' choice to employ the term "navigable waters" in the 1972 Clean Water Act simply continued nearly a century of usage. Viewed in light of the history of federal water regulation, the broad § 502(7) definition, and Congress' unambiguous instructions in the Conference Report, it is clear that the term "navigable waters" operates in the statute as a shorthand for "waters over which federal authority may properly be asserted."

*183 II

As the majority correctly notes, ante, at 168, when the Corps first promulgated regulations pursuant to § 404 of the 1972 Act, it construed its authority as being essentially the same as it had been under the 1899 RHA.^[8] The reaction to those regulations in the federal courts,^[9] in the Environmental Protection Agency (EPA),^[10] and in Congress^[11] convinced *184 the Corps that the statute required it "to protect water quality to the full extent of the [C]ommerce [C]lause" and to extend federal regulation over discharges "to many areas that have never before been subject to Federal permits or to this form of water quality protection." 40 Fed. Reg. 31320 (1975).

In 1975, the Corps therefore adopted the interim regulations that we upheld in Riverside Bayview. As we noted in that case, the new regulations understood "the waters of the United States" to include, not only navigable waters and their tributaries, but also "nonnavigable intrastate waters whose use or misuse could affect interstate commerce." 474 U. S., at 123. The 1975 regulations provided that the new program would become effective in three phases: phase 1, which became effective immediately, encompassed the navigable waters covered by the 1974 regulation and the RHA; phase 2, effective after July 1, 1976, extended Corps jurisdiction to nonnavigable tributaries, freshwater wetlands adjacent to primary navigable waters, and lakes; and phase 3, effective after July 1, 1977, extended Corps jurisdiction to all other waters covered under the statute, including any waters not covered by phases 1 and 2 (such as "intermittent rivers, streams, tributaries, and perched wetlands that are not contiguous or adjacent to navigable waters") that "the District Engineer determines necessitate regulation for the protection of water quality." 40 Fed. Reg. 31325-31326 (1975). The final version of these regulations, adopted in 1977, made clear that the covered waters included "isolated lakes and wetlands, intermittent streams, prairie potholes, and other waters that are not part of a tributary system to interstate waters or to navigable waters of the United States, the degradation or destruction of which could affect interstate commerce."^[12]

*185 The Corps' broadened reading of its jurisdiction provoked opposition among some Members of Congress. As a result, in 1977, Congress considered a proposal that would have limited the Corps' jurisdiction under § 404 to waters that are used, or by reasonable improvement could be used, as a means to transport interstate or foreign commerce and their adjacent wetlands. H. R. 3199, 95th Cong., 1st Sess., § 16(f) (1977). A bill embodying that proposal passed the House but was defeated in the Senate. The debates demonstrate that Congress was fully aware of the Corps' understanding of the scope of its jurisdiction under the 1972 Act. We summarized these debates in our opinion in Riverside Bayview:

"In both Chambers, debate on the proposals to narrow the definition of navigable waters centered largely on the issue of wetlands preservation. See [123 Cong. Rec.], at 10426-10432 (House debate); id., at 26710-26729 (Senate debate). Proponents of a more limited § 404 jurisdiction contended that the Corps' assertion of jurisdiction over wetlands and other nonnavigable `waters' had far exceeded what Congress had intended in enacting § 404. Opponents of the proposed changes argued that a narrower definition of `navigable waters' for purposes of § 404 would exclude vast stretches of crucial wetlands from the Corps' jurisdiction, with detrimental effects on wetlands ecosystems, w