This case presents the question whether the Clean Water Act (CWA), 33 U. S. C. § 1251 et seq., together with certain regulations promulgated under its authority by the Army Corps of Engineers, authorizes the Corps to require landowners to obtain permits from the Corps before discharging fill material into wetlands adjacent to navigable bodies of water and their tributaries.
The relevant provisions of the Clean Water Act originated in the Federal Water Pollution Control Act Amendments of 1972, 86 Stat. 816, and have remained essentially unchanged since that time. Under §§ 301 and 502 of the Act, 33 U. S. C. §§ 1311 and 1362, any discharge of dredged or fill materials into "navigable waters" — defined as the "waters of the United States" — is forbidden unless authorized by a permit issued by the Corps of Engineers pursuant to § 404, 33 U. S. C. § 1344.
In 1982, the 1977 regulations were replaced by substantively identical regulations that remain in force today. See 33 CFR § 323.2 (1985).
Respondent Riverside Bayview Homes, Inc. (hereafter respondent), owns 80 acres of low-lying, marshy land near the shores of Lake St. Clair in Macomb County, Michigan. In 1976, respondent began to place fill materials on its property as part of its preparations for construction of a housing development. The Corps of Engineers, believing that the property was an "adjacent wetland" under the 1975 regulation defining "waters of the United States," filed suit in the United States District Court for the Eastern District of Michigan, seeking to enjoin respondent from filling the property without the permission of the Corps.
Respondent again appealed, and the Sixth Circuit reversed. 729 F.2d 391 (1984). The court construed the Corps' regulation to exclude from the category of adjacent wetlands — and hence from that of "waters of the United States" — wetlands that were not subject to flooding by adjacent navigable waters at a frequency sufficient to support the growth of aquatic vegetation. The court adopted this construction of the regulation because, in its view, a broader definition of wetlands might result in the taking of private property without just compensation. The court also expressed its doubt that Congress, in granting the Corps jurisdiction to regulate the filling of "navigable waters," intended to allow regulation of wetlands that were not the result of flooding by navigable waters.
The question whether the Corps of Engineers may demand that respondent obtain a permit before placing fill material on its property is primarily one of regulatory and statutory interpretation: we must determine whether respondent's property is an "adjacent wetland" within the meaning of the applicable regulation, and, if so, whether the Corps' jurisdiction over "navigable waters" gives it statutory authority to regulate discharges of fill material into such a wetland. In this connection, we first consider the Court of Appeals' position that the Corps' regulatory authority under the statute and its implementing regulations must be narrowly construed to avoid a taking without just compensation in violation of the Fifth Amendment.
We have frequently suggested that governmental land-use regulation may under extreme circumstances amount to a "taking" of the affected property. See, e. g., Williamson County Regional Planning Comm'n v. Hamilton Bank, 473 U.S. 172 (1985); Penn Central Transportation Co. v. New York City, 438 U.S. 104 (1978). We have never precisely defined those circumstances, see id., at 123-128; but our general approach was summed up in Agins v. Tiburon, 447 U.S. 255, 260 (1980), where we stated that the application of landuse regulations to a particular piece of property is a taking only "if the ordinance does not substantially advance legitimate state interests . . . or denies an owner economically viable use of his land." Moreover, we have made it quite clear that the mere assertion of regulatory jurisdiction by a governmental body does not constitute a regulatory taking. See Hodel v. Virginia Surface Mining & Reclamation Assn., 452 U.S. 264,
If neither the imposition of the permit requirement itself nor the denial of a permit necessarily constitutes a taking, it follows that the Court of Appeals erred in concluding that a narrow reading of the Corps' regulatory jurisdiction over wetlands was "necessary" to avoid "a serious taking problem." 729 F. 2d, at 398.
Purged of its spurious constitutional overtones, the question whether the regulation at issue requires respondent to obtain a permit before filling its property is an easy one. The regulation extends the Corps' authority under § 404 to all wetlands adjacent to navigable or interstate waters and their tributaries. Wetlands, in turn, are defined as lands that are "inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions." 33 CFR § 323.2(c) (1985) (emphasis added). The plain language of the regulation refutes the Court of Appeals' conclusion that inundation or "frequent flooding" by the adjacent body of water is a sine qua non of a wetland under the regulation. Indeed, the regulation could hardly state more clearly that saturation by either surface or ground water is sufficient to bring an area within the category of wetlands, provided that
The history of the regulation underscores the absence of any requirement of inundation. The interim final regulation that the current regulation replaced explicitly included a requirement of "periodi[c] inundation." 33 CFR § 209.120(d)(2)(h) (1976). In deleting the reference to "periodic inundation" from the regulation as finally promulgated, the Corps explained that it was repudiating the interpretation of that language "as requiring inundation over a record period of years." 42 Fed. Reg. 37128 (1977). In fashioning its own requirement of "frequent flooding" the Court of Appeals improperly reintroduced into the regulation precisely what the Corps had excised.
Without the nonexistent requirement of frequent flooding, the regulatory definition of adjacent wetlands covers the property here. The District Court found that respondent's property was "characterized by the presence of vegetation that requires saturated soil conditions for growth and reproduction,"
An agency's construction of a statute it is charged with enforcing is entitled to deference if it is reasonable and not in conflict with the expressed intent of Congress. Chemical Manufacturers Assn. v. Natural Resources Defense Council, Inc., 470 U.S. 116, 125 (1985); Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 842-845 (1984). Accordingly, our review is limited to the question whether it is reasonable, in light of the language, policies, and legislative history of the Act for the Corps to exercise jurisdiction over wetlands adjacent to but not regularly flooded by rivers, streams, and other hydrographic features more conventionally identifiable as "waters."
Faced with such a problem of defining the bounds of its regulatory authority, an agency may appropriately look to the legislative history and underlying policies of its statutory grants of authority. Neither of these sources provides unambiguous guidance for the Corps in this case, but together they do support the reasonableness of the Corps' approach of defining adjacent wetlands as "waters" within the meaning of § 404(a). Section 404 originated as part of the Federal Water Pollution Control Act Amendments of 1972, which constituted a comprehensive legislative attempt "to restore and maintain the chemical, physical, and biological integrity of the Nation's waters." CWA § 101, 33 U. S. C. § 1251. This objective incorporated a broad, systemic view of the goal of maintaining and improving water quality: as the House Report on the legislation put it, "the word `integrity' . . . refers to a condition in which the natural structure and function of ecosystems [are] maintained." H. R. Rep. No. 92-911, p. 76 (1972). Protection of aquatic ecosystems, Congress recognized,
In keeping with these views, Congress chose to define the waters covered by the Act broadly. Although the Act prohibits discharges into "navigable waters," see CWA §§ 301(a), 404(a), 502(12), 33 U. S. C. §§ 1311(a), 1344(a), 1362(12), the Act's definition of "navigable waters" as "the waters of the United States" makes it clear that the term "navigable" as used in the Act is of limited import. In adopting this definition of "navigable waters," Congress evidently intended to repudiate limits that had been placed on federal regulation by earlier water pollution control statutes and to exercise its powers under the Commerce Clause to regulate at least some waters that would not be deemed "navigable" under the classical understanding of that term. See S. Conf. Rep. No. 92-1236, p. 144 (1972); 118 Cong. Rec. 33756-33757 (1972) (statement of Rep. Dingell).
Of course, it is one thing to recognize that Congress intended to allow regulation of waters that might not satisfy traditional tests of navigability; it is another to assert that Congress intended to abandon traditional notions of "waters" and include in that term "wetlands" as well. Nonetheless, the evident breadth of congressional concern for protection of water quality and aquatic ecosystems suggests that it is reasonable for the Corps to interpret the term "waters" to encompass wetlands adjacent to waters as more conventionally defined. Following the lead of the Environmental Protection Agency, see 38 Fed. Reg. 10834 (1973), the Corps has determined that wetlands adjacent to navigable waters do as a general matter play a key role in protecting and enhancing water quality:
We cannot say that the Corps' conclusion that adjacent wetlands are inseparably bound up with the "waters" of the United States — based as it is on the Corps' and EPA's technical expertise — is unreasonable. In view of the breadth of federal regulatory authority contemplated by the Act itself and the inherent difficulties of defining precise bounds to regulable waters, the Corps' ecological judgment about the relationship between waters and their adjacent wetlands provides an adequate basis for a legal judgment that adjacent wetlands may be defined as waters under the Act.
This holds true even for wetlands that are not the result of flooding or permeation by water having its source in adjacent bodies of open water. The Corps has concluded that wetlands may affect the water quality of adjacent lakes, rivers, and streams even when the waters of those bodies do not actually inundate the wetlands. For example, wetlands that are not flooded by adjacent waters may still tend to drain into those waters. In such circumstances, the Corps has concluded that wetlands may serve to filter and purify water draining into adjacent bodies of water, see 33 CFR § 320.4(b)(2)(vii) (1985), and to slow the flow of surface runoff into lakes, rivers, and streams and thus prevent flooding and erosion, see §§ 320.4(b)(2)(iv) and (v). In addition, adjacent wetlands may "serve significant natural biological functions, including food chain production, general habitat, and nesting,
Following promulgation of the Corps' interim final regulations in 1975, the Corps' assertion of authority under § 404 over waters not actually navigable engendered some congressional opposition. The controversy came to a head during Congress' consideration of the Clean Water Act of 1977, a major piece of legislation aimed at achieving "interim improvements within the existing framework" of the Clean Water Act. H. R. Rep. No. 95-139, pp. 1-2 (1977). In the
Critics of the Corps' permit program attempted to insert limitations on the Corps' § 404 jurisdiction into the 1977 legislation: the House bill as reported out of committee proposed a redefinition of "navigable waters" that would have limited the Corps' authority under § 404 to waters navigable in fact and their adjacent wetlands (defined as wetlands periodically inundated by contiguous navigable waters). H. R. 3199, 95th Cong., 1st Sess., § 16 (1977). The bill reported by the Senate Committee on Environment and Public Works, by contrast, contained no redefinition of the scope of the "navigable waters" covered by § 404, and dealt with the perceived problem of overregulation by the Corps by exempting certain activities (primarily agricultural) from the permit requirement and by providing for assumption of some of the Corps' regulatory duties by federally approved state programs. S. 1952, 95th Cong., 1st Sess., § 49(b) (1977). On the floor of the Senate, however, an amendment was proposed limiting the scope of "navigable waters" along the lines set forth in the House bill. 123 Cong. Rec. 26710-26711 (1977).
In both Chambers, debate on the proposals to narrow the definition of navigable waters centered largely on the issue of wetlands preservation. See id., 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 nonavigable "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, water quality, and the aquatic environment generally. The debate, particularly in the Senate, was lengthy. In the House, the debate ended with the adoption of a narrowed definition of "waters"; but in the Senate the limiting
The significance of Congress' treatment of the Corps' § 404 jurisdiction in its consideration of the Clean Water Act of 1977 is twofold. First, the scope of the Corps' asserted jurisdiction over wetlands was specifically brought to Congress' attention, and Congress rejected measures designed to curb the Corps' jurisdiction in large part because of its concern that protection of wetlands would be unduly hampered by a narrowed definition of "navigable waters." Although we are chary of attributing significance to Congress' failure to act, a refusal by Congress to overrule an agency's construction of legislation is at least some evidence of the reasonableness of that construction, particularly where the administrative construction has been brought to Congress' attention through legislation specifically designed to supplant it. See Bob Jones University v. United States, 461 U.S. 574, 599-601 (1983); United States v. Rutherford, 442 U.S. 544, 554, and n. 10 (1979).
Second, it is notable that even those who would have restricted the reach of the Corps' jurisdiction would have done so not by removing wetlands altogether from the definition of "waters of the United States," but only by restricting the scope of "navigable waters" under § 404 to waters navigable in fact and their adjacent wetlands. In amending the definition of "navigable waters" for purposes of § 404 only, the backers of the House bill would have left intact the existing definition of "navigable waters" for purposes of § 301 of the
Two features actually included in the legislation that Congress enacted in 1977 also support the view that the Act authorizes the Corps to regulate discharges into wetlands. First, in amending § 404 to allow federally approved state permit programs to supplant regulation by the Corps of certain discharges of fill material, Congress provided that the States would not be permitted to supersede the Corps' jurisdiction to regulate discharges into actually navigable waters and waters subject to the ebb and flow of the tide, "including wetlands adjacent thereto." CWA § 404(g)(1), 33 U. S. C. § 1344(g)(1). Here, then, Congress expressly stated that the term "waters" included adjacent wetlands.
We are thus persuaded that the language, policies, and history of the Clean Water Act compel a finding that the Corps has acted reasonably in interpreting the Act to require permits for the discharge of fill material into wetlands adjacent to the "waters of the United States." The regulation in which the Corps has embodied this interpretation by its terms includes the wetlands on respondent's property within the class of waters that may not be filled without a permit; and, as we have seen, there is no reason to interpret the regulation more narrowly than its terms would indicate. Accordingly, the judgment of the Court of Appeals is