ents. With him on the brief were Richard Cotton and David E. Engdahl.*

MR. JUSTICE MARSHALL delivered the opinion of the Court.

The issue in this case is whether the Environmental Protection Agency (EPA) has the authority under the Federal Water Pollution Control Act (FWPCA), as amended in 1972, 86 Stat. 816, 33 U. S. C. § 1251 et seq. (1970 ed., Supp. IV), to regulate the discharge into the

*Henry V. Nickel and Marx Leva filed a brief for the Boston Edison Co. et al. as amici curiae urging reversal.

Michael S. Baram, pro se, filed a brief for Michael S. Baram et al. as amici curiae urging affirmance.

A brief of amici curiae was filed by Evelle J. Younger, Attorney General, Robert H. O'Brien, Assistant Attorney General, and Nicholas C. Yost, C. Foster Knight, and Janet I. Motley, Deputy Attorneys General, for the State of California, joined by the Attorneys General and other officials for their respective States as follows: John P. Moore, Attorney General of Colorado, and David Robbins, First Assistant Attorney General; Robert L. Shevin, Attorney General of Florida, and Kenneth F. Hoffman, Assistant Attorney General; Curt Schneider, Attorney General of Kansas, and Thomas Wobker, Assistant Attorney General; Francis B. Burch, Attorney General of Maryland, and Warren K. Rich, Assistant Attorney General; Francis X. Bellotti, Attorney General of Massachusetts; Frank J. Kelley, Attorney General of Michigan, Robert A. Derengoski, Solicitor General, and Stewart H. Freeman, Assistant Attorney General; Warren R. Spannaus, Attorney General of Minnesota, Peter W. Sipkins, Solicitor General, and Eldon G. Kaul, Assistant Attorney General; John C. Danforth, Attorney General of Missouri, and Robert M. Lindholm, Assistant Attorney General; Warren B. Rudman, Attorney General of New Hampshire, and Donald Stever, Assistant Attorney General; Louis J. Lefkowitz, Attorney General of New York, and John Shea III, Assistant Attorney General; Michael Alushin, Attorney General of Pennsylvania; John L. Hill, Attorney General of Texas, and Douglas Caroom, Assistant Attorney General; and Slade Gorton, Attorney General of Washington, and Charles B. Roe, Senior Assistant Attorney General.

209-904 - 78 - 4

Nation's waterways of nuclear waste materials subject to regulation by the Atomic Energy Commission (AEC) and its successors under the Atomic Energy Act of 1954 (AEA). 68 Stat. 919, as amended, 42 U. S. C. § 2011 et seq. In statutory terms, the question is whether these nuclear materials are "pollutants" within the meaning of the FWPCA.

I

Respondents are Colorado-based organizations and Colorado residents who claim potential harm from the discharge of radioactive effluents from two nuclear plants the Fort St. Vrain Nuclear Generating Station and the Rocky Flats nuclear weapons components plant. These facilities are operated in conformity with radioactive effluent standards imposed by the AEC pursuant to the Atomic Energy Act. The dispute in this case arises because the EPA has disclaimed any authority under the FWPCA to set standards of its own to govern the discharge of radioactive materials subject to regulation under the AEA. Respondents, taking issue with the EPA's disclaimer of authority, brought this suit against petitioners, the EPA and its Administrator, under § 505 of the FWPCA, 33 U. S. C. § 1365 (1970 ed., Supp. IV), which authorizes "citizen suits" against the Administrator for failure to perform nondiscretionary duties under the FWPCA. They sought a declaration that the definition of a "pollutant" under the FWPCA encompasses all radioactive materials, including those regulated under the terms of the AEA, and an injunction directing the EPA and its Administrator to regulate the discharge of all such radioactive materials.

On cross-motions for summary judgment, the United States District Court for the District of Colorado held that the AEC had exclusive authority to regulate discharges of radioactive materials covered by the AEA.

373 F. Supp. 991 (1974). The Court of Appeals for the Tenth Circuit reversed, holding that the FWPCA requires the EPA to regulate discharges into the Nation's waters of all radioactive materials, including those covered by the AEA. 507 F. 2d 743 (1974). Because of the importance of the issue involved in this case, we granted certiorari. 421 U. S. 998 (1975). We now

reverse.

II

Since 1946, when the first Atomic Energy Act was passed, 60 Stat. 755, the Federal Government has exercised control over the production and use of atomic energy through the AEC-replaced since the commencement of this litigation by the Nuclear Regulatory Commission (NRC) and the Energy Research and Development Administration (ERDA). Under the AEA, private parties are permitted to engage in the production of atomic energy for industrial or commercial purposes, but only in accordance with licenses issued by the AEC (NRC) in the furtherance of the purposes of the Act. 42 U. S. C. § 2133.

The comprehensive regulatory scheme created by the AEA embraces the production, possession, and use of three types of radioactive materials-source material,

1 Under the Energy Reorganization Act of 1974, 88 Stat. 1233, 42 U. S. C. § 5801 et seq. (1970 ed., Supp. IV), the licensing and related regulatory functions of the AEC were transferred to the NRC; the ERDA assumed responsibility for the operation of Government nuclear research and production facilities. 42 U. S. C. §§ 5841 (f), 5842, 5814 (c) (1970 ed., Supp. IV). We will refer generally to the AEC to cover the NRC and ERDA after their formation, except where the context requires specific designation of the NRC or ERDA.

2 "The term 'source material' means (1) uranium, thorium, or any other material which is determined by the Commission pursuant to the provisions of section 2091 of this title to be source material;

special nuclear material, and byproduct material. In carrying out its regulatory duties under the AEA, the AEC is authorized to establish "such standards . . . as [it] may deem necessary or desirable . . . to protect health or to minimize danger to life or property." 42 U. S. C. § 2201 (b). See also 42 U. S. C. §§ 2073 (b), (e), 2093 (b), 2111, 2133 (a), (d), 2134 (d). Pursuant to this authority, the AEC (NRC) has established by regulation maximum permissible releases of source, byproduct, and special nuclear materials into the environment by licensees. 10 CFR § 20.106 and App. B, Table II (1976). The regulations further provide that licensees should, in addition to complying with the established limits, "make every reasonable effort to maintain . . . releases of radioactive materials in effluents . . . as low as is reasonably achievable." 10 CFR § 20.1 (c) (1976). Similarly, the regulations require that nuclear facilities be designed to keep levels of radioactive material in effluents "as low as is reasonably achievable." 10 CFR § 50.34a (1976). See also 10 CFR §§ 50.36a, 50.57 (a) (3), (6) (1976).5

or (2) ores containing one or more of the foregoing materials, in such concentration as the Commission may by regulation determine from time to time." 42 U. S. C. § 2014 (z).

3 "The term 'special nuclear material' means (1) plutonium, uranium enriched in the isotope 233 or in the isotope 235, and any other material which the Commission, pursuant to the provisions of section 2071 of this title, determines to be special nuclear material, but does not include source material; or (2) any material artificially enriched by any of the foregoing, but does not include source material." 42 U. S. C. § 2014 (aa).

4 "The term 'byproduct material' means any radioactive material (except special nuclear material) yielded in or made radioactive by exposure to the radiation incident to the process of producing or utilizing special nuclear material." 42 U. S. C. § 2014 (e).

5 The Fort St. Vrain Nuclear Generating Station is owned and operated by an NRC licensee, and is accordingly bound by the AEC (NRC) regulations. The Rocky Flats plant is a federal

The FWPCA established a regulatory program to control and abate water pollution, stating as its ultimate objective the elimination of all discharges of "pollutants" into the navigable waters by 1985. In furtherance of this objective, the FWPCA calls for the achievement of effluent limitations that require applications 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) (1970 ed., Supp. IV). These effluent limitations are enforced through a permit program. The discharge of "pollutants" into water is unlawful without a permit issued by the Administrator of the EPA or, if a State has developed a program that complies with the FWPCA, by the State. 33 U. S. C. §§ 1311 (a), 1342 (1970 ed., Supp. IV).

The term "pollutant" is defined by the FWPCA to include, inter alia, "radioactive materials." But when

facility operated for the ERDA by a private contractor to fabricate plutonium into nuclear weapon parts. The ERDA is also responsible for the operation of approximately 24 other facilities that discharge low levels of source, byproduct, and special nuclear materials. of these facilities are required to conform to the same effluent standards established by the NRC for commercial facilities. Executive Order No. 11752, § 4 (a) (6), 3 CFR, p. 384 (1974).

The permit program of Colorado, where this case originated, was approved by the EPA on April 8, 1975. 40 Fed. Reg. 16713. "The term 'pollutant' means dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water. This term does not mean (A) 'sewage from vessels' within the meaning of section 1322 of this title; or (B) water, gas, or other material which is injected into a well to facilitate production of oil or gas, or water derived in association with oil or gas production and disposed of in a well, if the well used either to facilitate production or for disposal purposes is approved by authority of the State in which the well is