delivered the opinion of the Court.
This сase 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.
HH
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 Cоrps of Engineers pursuant to § 404, 33 U. S. C. § 1344.
1
After initially construing the Act to cover only waters navigable in fact, in 1975 the Corps issued interim final regulations redefining “the waters of the United States” to include not only actually navigable waters but also tributaries of such waters, interstate waters and their tributaries, and nonnavigable intrastate waters whose use or misuse could affect interstate commerce. 40 Fed. Reg. 31320
“The term ‘wetlands’ means those areas 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 fife in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas.” 33 CFR §323.2(c) (1978).
In 1982, the 1977 regulations were replaced by substantively identical regulations that remain in force today. See 33 CFR §323.2 (1985). 2
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.
M h — I
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 rеspondent’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,
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.”
Ill
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 arе “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)(7t) (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. 7
Without the nonexistent requirement of frequent flоoding, 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 re
> J — I
A
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.,
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 recog
In keeping with these views, Congress chosе 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:
“The regulation of activities that cause water pollution cannot rely on . . . artificial lines . . . but must focus on all waters that together form the entire aquatic system.Water moves in hydrologic cycles, and the pollution of this part of the aquatic system, regardless of whether it is above or below an ordinary high water mark, or mean high tide line, will affect the water quality of the other waters within that aquatic system.
“For this reason, the landward limit of Federal jurisdiction under Section 404 must include any adjacent wetlands that form the border of or аre in reasonable proximity to other waters of the United States, as these wetlands are part of this aquatic system.” 42 Fed. Reg. 37128 (1977).
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 adjaсent 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 surfacе 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,
B
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 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, water quality, and the aquatic environment generally. The debate, particularly in the Senate, was lengthy. In the House, the debate ended with thе 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,
Second, it is notable that еven 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 statеd that the term “waters” included adjacent wetlands.
11
Second, the
C
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
Reversed.
Notes
With respect to certain waters, the Corps’ authority may be transferred to States that have devised federally aрproved permit programs. CWA § 404(g), as added, 91 Stat. 1600, 33 U. S. C. § 1344(g). Absent such an approved program, the Corps retains jurisdiction under § 404 over all “waters of the United States.”
The regulations also cover certain wetlands not necessarily adjacent to other waters. See 33 CFR §§ 323.2(a)(2) and (3) (1985). These provisions are not now before us.
In denying the Government’s petition for rehearing, the panel reiterated somewhat more strongly its belief that the Corps’ construction of its regulation was “overbroad and inconsistent with the language of the Act.”
Even were the Court of Appeals correct in concluding that a narrowing construction of the regulation is necessary to avoid takings of property through the application of the permit requirement, the construction adopted — which requires a showing of frequent flooding before property may be classified as a wetland — is hardly tailored to the supposed difficulty. Whether the denial of a permit would constitute a taking in any given case would depend upon the effect of the denial on the owner’s ability to put the property to productive use. Whether the property was frequently flooded would have no particular bearing on this question, for overbroad regulation of even completely submerged property may constitute a taking. See, e.
g., Kaiser Aetna
v.
United States,
United States
v.
Security Industrial Bank,
Because the Corps has now denied respondent a permit to fill its property, respondent may well have a ripe claim that a taking has occurred. On the record before us, however, we have no basis for evaluating this claim, because no evidence has been introduced that bears on the question of the extent to which denial of a permit to fill this property will prevent economically viable uses of the property or frustrate reasonable investment-backed expectations. In any event, this lawsuit is not the proper forum for resolving such a dispute: if the Corps has indeed effectively taken respondent’s property, respondent’s proper course is not to resist the Corps’ suit for enforcement by denying that the regulation covers the property, but to initiate a suit for compensation in the Claims Court. In so stating, of course, we do not rule that respondent will be entitled to compensation for any temporary denial of use of its property should the Corps ultimately relent and allow it to be filled. We have not yet resolved the question whether compensation is a constitutionally mandated remedy for “temporary regulatory takings,” see
Williamson County Planning Comm’n
v.
Hamilton Bank,
The Court of Appeals seems also to have rested its frequent-flooding requirement on the language in the regulation stating that wetlands encompass those areas that “under normal circumstances do support” aquatic or semiaquatic vegetation. In the preamble to the final regulation, the Corps explained that this language was intended in part to exclude areas characterized by the “abnormal presence of aquatic vegetation in a non-aquatic area.” 42 Fed. Reg. 37128 (1977). Apparently, the Court of Appeals concluded that the growth of wetlands vegetation in soils saturated by ground water rather than flooded by waters emanating from an adjacent navigable water or its tributaries was “аbnormal” within the meaning of the preamble. This interpretation is untenable in light of the explicit statements in both the regulation and its preamble that areas saturated by ground water can fall within the category of wetlands. It would be nonsensical for the Corps to define wetlands to include such areas and then in the same sentence exclude them on the ground that the presence of wetland vegetation in such areas was abnormal. Evidently, the Corps had something else in mind when it referred to “abnormal” growth of wetlands vegetation — namely, the aberrational presence of such vegetation in dry, upland areas.
We are not called upon to address the quеstion of the authority of the Corps to regulate discharges of fill material into wetlands that are not adja
Of course, it may well be that not every adjacent wetland is of great importance to the environment of adjoining bodies of water. But the existence of such cases does not seriously undermine the Corps’ decision to define all adjacent wetlands as “waters.” If it is reasonable for the Corps to conclude that in the majority of cases, adjacent wetlands have significant effects on water quality and the aquatic ecosystem, its dеfinition can stand. That the definition may include some wetlands that are not significantly intertwined with the ecosystem of adjacent waterways is of little moment, for where it appears that a wetland covered by the Corps’ definition is in fact lacking in importance to the aquatic environment — or where its importance is outweighed by other values — the Corps may always allow development of the wetland for other uses simply by issuing a permit. See 33 CFR § 320.4(b)(4) (1985).
123 Cong. Rec. 39209 (1977); see also id., at 39210 (statement of Sen. Wallop); id., at 39196 (statement of Sen. Randolph); id., at 38950 (statement of Rep. Murphy); id., at 38994 (statement of Rep. Ambro).
To be sure, §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”); however, in light of the fact that the various provisions of the Act should be read in pari materia, it does at least suggest strongly that the term “waters” as used in the Act does not necessarily exclude “wetlands.”