An in

Co. v. Mesa Canal Co., 177 U. S. 296, 302 (1900). junction should issue only where the intervention of a court of equity "is essential in order effectually to protect property rights against injuries otherwise irremediable." Cavanaugh v. Looney, 248 U. S. 453, 456 (1919). The Court has repeatedly held that the basis for injunctive relief in the federal courts has always been irreparable injury and the inadequacy of legal remedies. Rondeau v. Mosinee Paper Corp., 422 U. S. 49, 61 (1975); Sampson v. Murray, 415 U. S. 61, 88 (1974); Beacon Theaters, Inc. v. Westover, 359 U. S. 500, 506-507 (1959); Hecht Co. v. Bowles, supra, at 329.

Where plaintiff and defendant present competing claims of injury, the traditional function of equity has been to arrive at a "nice adjustment and reconciliation" between the competing claims, Hecht Co. v. Bowles, supra, at 329. In such cases, the court "balances the conveniences of the parties and possible injuries to them according as they may be affected by the granting or withholding of the injunction." Yakus v. United States, 321 U. S. 414, 440 (1944). "The essence of equity jurisdiction has been the power of the Chancellor to do equity and to mould each decree to the necessities of the particular case. Flexibility rather than rigidity has distinguished it." Hecht Co. v. Bowles, supra, at 329.

In exercising their sound discretion, courts of equity should pay particular regard for the public consequences in employing the extraordinary remedy of injunction. Railroad Comm'n v. Pullman Co., 312 U. S. 496, 500 (1941). Thus, the Court has noted that "[t]he award of an interlocutory injunction by courts of equity has never been regarded as strictly a matter of right, even though irreparable injury may otherwise result to the plaintiff," and that “where an injunction is asked which will adversely affect a public interest for whose impairment, even temporarily, an injunction bond cannot compensate, the court may in the public interest withhold relief until a final determination of the rights of the parties, though the postponement may be burdensome to the

plaintiff." Yakus v. United States, supra, at 440 (footnote omitted). The grant of jurisdiction to ensure compliance with a statute hardly suggests an absolute duty to do so under any and all circumstances, and a federal judge sitting as chancellor is not mechanically obligated to grant an injunction for every violation of law. TVA v. Hill, 437 U. S., at

193; Hecht Co. v. Bowles, 321 U. S., at 329.

These commonplace considerations applicable to cases in which injunctions are sought in the federal courts reflect a "practice with a background of several hundred years of history," Hecht Co. v. Bowles, supra, at 329, a practice of which Congress is assuredly well aware. Of course, Congress may intervene and guide or control the exercise of the courts' discretion, but we do not lightly assume that Congress has intended to depart from established principles. Hecht Co. v. Bowles, supra, at 329. As the Court said in Porter v. Warner Holding Co., 328 U. S. 395, 398 (1946):

"Moreover, the comprehensiveness of this equitable jurisdiction is not to be denied or limited in the absence of a clear and valid legislative command. Unless a statute in so many words, or by a necessary and inescapable inference, restricts the court's jurisdiction in equity, the full scope of that jurisdiction is to be recognized and applied. "The great principles of equity, securing complete justice, should not be yielded to light inferences, or doubtful construction.' Brown v. Swann, 10 Pet. 497, 503...

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In TVA v. Hill, we held that Congress had foreclosed the exercise of the usual discretion possessed by a court of equity. There, we thought that "[o]ne would be hard pressed to find a statutory provision whose terms were any plainer" than that before us. 437 U. S., at 173. The statute involved, the Endangered Species Act, 87 Stat. 884, 16 U. S. C. § 1531 et seq., required the District Court to enjoin completion of the Tellico Dam in order to preserve the snail

darter, a species of perch. The purpose and language of the statute under consideration in Hill, not the bare fact of a statutory violation, compelled that conclusion. Section 7 of the Act, 16 U. S. C. § 1536, requires federal agencies to “insure that actions authorized, funded, or carried out by them do not jeopardize the continued existence of [any] endangered species. . . or result in the destruction or modification of habitat of such species which is determined . . . to be critical." The statute thus contains a flat ban on the destruction of critical habitats.

It was conceded in Hill that completion of the dam would eliminate an endangered species by destroying its critical habitat. Refusal to enjoin the action would have ignored the "explicit provisions of the Endangered Species Act." 437 U. S., at 173. Congress, it appeared to us, had chosen the snail darter over the dam. The purpose and language of the statute limited the remedies available to the District Court; only an injunction could vindicate the objectives of the Act. That is not the case here. An injunction is not the only means of ensuring compliance. The FWPCA itself, for example, provides for fines and criminal penalties. 33 U. S. C. §§ 1319(c) and (d). Respondents suggest that failure to enjoin the Navy will undermine the integrity of the permit process by allowing the statutory violation to continue. The integrity of the Nation's waters, however, not the permit process, is the purpose of the FWPCA.' As Congress explained, the objective of the FWPCA is to "restore and maintain the chemical, physical, and biological integrity of the Nation's waters." 33 U. S. C. § 1251(a).

'The objective of this statute is in some respects similar to that sought in nuisance suits, where courts have fully exercised their equitable discretion and ingenuity in ordering remedies. E. g., Spur Industries, Inc. v. Del E. Webb Development Co., 108 Ariz. 178, 494 P. 2d 700 (1972); Boomer v. Atlantic Cement Co., 26 N. Y. 2d 219, 257 N. E. 2d 870 (1970).

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This purpose is to be achieved by compliance with the Act, including compliance with the permit requirements. Here, however, the discharge of ordnance had not polluted the waters, and, although the District Court declined to enjoin the discharges, it neither ignored the statutory violation nor undercut the purpose and function of the permit system. The court ordered the Navy to apply for a permit." It temporarily, not permanently, allowed the Navy to continue its activities without a permit.

In Hill, we also noted that none of the limited "hardship exemptions" of the Endangered Species Act would "even remotely apply to the Tellico Project." 437 U. S., at 188. The prohibition of the FWPCA against discharge of pollutants, in contrast, can be overcome by the very permit the Navy was ordered to seek.10 The Senate Report to the 1972

'Federal agencies must comply with the water pollution abatement requirements "in the same manner, and to the same extent as any nongovernmental entity. . . ." 33 U. S. C. § 1323(a) (1976 ed., Supp. IV). S. Rep. No. 92-414, p. 80 (1971), pointed to "[f]ederal agencies such as the Department of Defense" for failing to abate pollution.

"The Navy applied for an NPDES permit in December 1979. In May 1981, the EPA issued a draft NPDES permit and a notice of intent to issue that permit. The FWPCA requires a certification of compliance with state water quality standards before the EPA may issue an NPDES permit. 33 U. S. C. § 1341(a). The Environmental Quality Board of the Commonwealth of Puerto Rico denied the Navy a water quality certificate in connection with this application for an NPDES in June 1981. In February 1982, the Environmental Quality Board denied the Navy's reconsideration request and announced it was adhering to its original ruling. In a letter dated April 9, 1982, the Solicitor General informed the Clerk of the Court that the Navy has filed an action challenging the denial of the water quality certificate. United States v. Commonwealth of Puerto Rico, Civ. Action No. 82-0726 (Dist. Ct. PR).

"As we have explained, the 1972 Amendments to the FWPCA established the NPDES as

"a means of achieving and enforcing the effluent limitations. Under the NPDES, it is unlawful for any person to discharge a pollutant without obtaining a permit and complying with its terms. An NPDES permit serves

Amendments explains that the permit program would be enacted because "the Committee recognizes the impracticality of any effort to halt all pollution immediately." S. Rep. No. 92-414, p. 43 (1971). That the scheme as a whole contemplates the exercise of discretion and balancing of equities militates against the conclusion that Congress intended to deny courts their traditional equitable discretion in enforcing the statute.

Other aspects of the statutory scheme also suggest that Congress did not intend to deny courts the discretion to rely on remedies other than an immediate prohibitory injunction. Although the ultimate objective of the FWPCA is to eliminate all discharges of pollutants into the navigable waters by 1985, the statute sets forth a scheme of phased compliance. As enacted, it called for the achievement of the "best practicable control technology currently available" by July 1, 1977, and the "best available technology economically achievable" by July 1, 1983. 33 U. S. C. §1311(b). This scheme of phased compliance further suggests that this is a statute in which Congress envisioned, rather than curtailed, the exercise of discretion."

to transform generally applicable effluent limitations and other standards-including those based on water quality-into the obligations (including a timetable for compliance) of the individual discharger, and the Amendments provide for direct administrative and judicial enforcement of permits.... With few exceptions, for enforcement purposes a discharger in compliance with the terms and conditions of an NPDES permit is deemed to be in compliance with those sections of the Amendments on which the permit conditions are based. . . . In short, the permit defines, and facilitates compliance with, and enforcement of, a preponderance of a discharger's obligations under the Amendments." EPA v. California ex rel. State Water Resources Control Board, 426 U. S. 200, 205 (1976) (footnote omitted).

"We have, however, held some standards related to phased compliance to be absolute. See EPA v. National Crushed Stone Assn., 449 U. S. 64 (1980). In Middlesex County Sewerage Authority v. National Sea Clammers Assn., 453 U. S. 1 (1981), we concluded that the federal common law of nuisance was pre-empted by the FWPCA and other similar