S. D. WARREN CO. v. MAINE BOARD OF ENVIRON- MENTAL PROTECTION et al.

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370 OCTOBER TERM, 2005
Syllabus
S. D. WARREN CO. v. MAINE BOARD OF ENVIRON-
MENTAL PROTECTION et al.
certiorari to the supreme judicial court of maine
No. 04–1527. Argued February 21, 2006—Decided May 15, 2006
Petitioner company (Warren) asked the Federal Energy Regulatory Com
mission (FERC) to renew federal licenses for five of the hydroelectric
dams it operates on a Maine river to generate power for its paper mill.
Each dam impounds water, which is then run through turbines and re
turned to the riverbed, passing around a section of the river. Under
protest, Warren applied for water quality certifications from respondent
Maine Board of Environmental Protection pursuant to § 401 of the Clean
Water Act, which requires state approval of “any activity” “which may
result in any discharge into the [Nation’s] navigable waters.” FERC
licensed the dams subject to compliance with those certifications, which
require Warren to maintain a minimum stream flow and to allow passage
for certain fish and eels. After losing state administrative appeals,
Warren filed suit in a state court, which rejected Warren’s claim that its
dams do not result in a “discharge” under § 401. The State Supreme
Judicial Court affirmed.
Held: Because a dam raises a potential for a discharge, § 401 is triggered
and state certification is required. Pp. 375–387.
(a) The Clean Water Act does not define “discharge,” but provides
that the term “when used without qualification includes a discharge of
a pollutant, and a discharge of pollutants,” 33 U. S. C. § 1362(16). But
“discharge” is presumably broader, else superfluous, and since it is nei
ther defined nor a term of art, it should be construed “in accordance
with its ordinary or natural meaning,” FDIC v. Meyer, 510 U. S. 471,
476. When applied to water, discharge commonly means “flowing or
issuing out,” Webster’s New International Dictionary 742. This Court
has consistently intended that meaning in prior water cases, including
the only case focused on § 401, PUD No. 1 of Jefferson Cty. v. Washing
ton Dept. of Ecology, 511 U. S. 700, in which no one questioned that the
discharge of water from a dam fell within § 401’s ambit. The Environ
mental Protection Agency and FERC have also regularly read “dis
charge” to cover releases from hydroelectric dams. Pp. 375–378.
(b) Warren’s three arguments for avoiding this common reading are
unavailing. The canon noscitur a sociis—“a word is known by the
company it keeps,” Gustafson v. Alloyd Co., 513 U. S. 561, 575—does
not apply here. Warren claims that since “discharge” is keeping com

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Syllabus
pany with “discharge” defined as adding one or more pollutants, see
§ 1362(12), discharge standing alone must also require the addition of
something foreign to the water. This argument seems to assume that
pairing a broad statutory term with a narrow one shrinks the broad
one, but there is no such general usage of language this way. Warren
also relies on South Fla. Water Management Dist. v. Miccosukee Tribe,
541 U. S. 95, but that case is not on point. It addressed § 402, not § 401,
and the two sections are not interchangeable, as they serve different
purposes and use different language to reach them. Thus, that some
thing must be added in order to implicate § 402 does not explain what
suffices for a discharge under § 401. Finally, the Clean Water Act’s leg
islative history, if it means anything, goes against Warren’s reading of
“discharge.” Pp. 378–384.
(c) Warren’s arguments against reading “discharge” in its common
sense also miss the forest for the trees. Congress passed the Clean
Water Act to “restore and maintain the chemical, physical, and biological
integrity of the Nation’s waters,” 33 U. S. C. § 1251(a), the “national
goal” being to achieve “water quality [providing] for the protection and
propagation of fish . . . and . . . for recreation,” § 1251(a)(2). To do this,
the Act deals with “pollution” generally, see § 1251(b), which it defines
as “the man-made or man-induced alteration of the [water’s] chemical,
physical, biological, and radiological integrity,” § 1362(19). Because the
alteration of water quality as thus defined is a risk inherent in limiting
river flow and releasing water through turbines, changes in the river’s
flow, movement, and circulation fall within a State’s legitimate legisla
tive business. State certifications under § 401 are essential in the
scheme to preserve state authority to address the broad range of pollu
tion. Reading § 401 to give “discharge” its common and ordinary mean
ing preserves the state authority apparently intended. Pp. 384–387.
868 A. 2d 210, affirmed.
Souter, J., delivered the opinion of the Court, in which Roberts, C. J.,
and Stevens, Kennedy, Thomas, Ginsburg, Breyer, and Alito, JJ.,
joined, and in which Scalia, J., joined as to all but Part III–C.
William J. Kayatta, Jr., argued the cause for petitioner.
With him on the briefs was Matthew D. Manahan.
G. Steven Rowe, Attorney General of Maine, argued the
cause for respondents. With him on the brief for Maine
Board of Environmental Protection were Paul Stern, Deputy
Attorney General, and Carol A. Blasi and Gerald D. Reid,
Assistant Attorneys General. Richard J. Lazarus, Daniel

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372 S. D. WARREN CO. v. MAINE BD. OF
ENVIRONMENTAL PROTECTION
Counsel
H. Squire, Ethan G. Shenkman, Sean Mahoney, and Ronald
A. Shems filed a brief for American Rivers et al. as respond
ents under this Court’s Rule 12.6.
Jeffrey P. Minear argued the cause for the United States
as amicus curiae urging affirmance. With him on the brief
were Solicitor General Clement, Assistant Attorney Gen
eral Wooldridge, Deputy Solicitor General Hungar, Greer
S. Goldman, Ellen J. Durkee, John L. Smeltzer, and Ann
R. Klee.*
*Briefs of amici curiae urging reversal were filed for Augusta, Georgia,
by George A. Somerville; for the Edison Electric Institute et al. by Jeffrey
L. Fisher, Daniel M. Adamson, Edward H. Comer, Kristy A. N. Bulleit,
James H. Hancock, Jr., and Richard S. Wasserstrom; for the National
Association of Home Builders et al. by Virginia S. Albrecht, Karma B.
Brown, Kathy Robb, Duane J. Desiderio, and Thomas Jon Ward; for the
New England Legal Foundation by Martin J. Newhouse, Andrew R.
Grainger, and Michael E. Malamut; and for the Salt River Project Ag
ricultural Improvement and Power District by John B. Weldon, Jr., and
Lisa M. McKnight.
Briefs of amici curiae urging affirmance were filed for the State of New
York et al. by Eliot Spitzer, Attorney General of New York, Caitlin J.
Halligan, Solicitor General, Robert H. Easton, Deputy Solicitor General,
Peter H. Lehner, Gregory Silbert, Assistant Solicitor General, and James
M. Tierney, Assistant Attorney General, by Rob McKenna, Attorney Gen
eral of Washington, and Brian Faller and Ron Lavigne, Assistant Attor
neys General, by Roberto J. Sa´ nchez Ramos, Secretary of Justice of
Puerto Rico, by Susan Shinkman, and by the Attorneys General for their
respective States as follows: David W. Ma´ rquez of Alaska, Terry Goddard
of Arizona, Bill Lockyer of California, Richard Blumenthal of Connecti
cut, Carl C. Danberg of Delaware, Mark J. Bennett of Hawaii, Lisa Madi
gan of Illinois, Thomas J. Miller of Iowa, Gregory D. Stumbo of Kentucky,
Charles C. Foti, Jr., of Louisiana, J. Joseph Curran, Jr., of Maryland,
Thomas F. Reilly of Massachusetts, Michael A. Cox of Michigan, Mike
Hatch of Minnesota, Jeremiah W. (Jay) Nixon of Missouri, Mike McGrath
of Montana, George J. Chanos of Nevada, Kelly A. Ayotte of New Hamp
shire, Peter C. Harvey of New Jersey, Patricia A. Madrid of New Mexico,
Roy Cooper of North Carolina, W. A. Drew Edmondson of Oklahoma,
Hardy Myers of Oregon, Patrick C. Lynch of Rhode Island, Henry Mc-
Master of South Carolina, Lawrence E. Long of South Dakota, Paul G.
Summers of Tennessee, Mark L. Shurtleff of Utah, William H. Sorrell of

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373 Cite as: 547 U. S. 370 (2006)
Opinion of the Court
Justice Souter delivered the opinion of the Court.†
The issue in this case is whether operating a dam to
produce hydroelectricity “may result in any discharge into
the navigable waters” of the United States. If so, a federal
license under § 401 of the Clean Water Act requires state
certification that water protection laws will not be violated.
We hold that a dam does raise a potential for a discharge,
and state approval is needed.
I
The Presumpscot River runs through southern Maine from
Sebago Lake to Casco Bay, and in the course of its 25 miles
petitioner, S. D. Warren Company, operates several hydro
power dams to generate electricity for its paper mill. Each
dam creates a pond, from which water funnels into a “power
canal,” through turbines, and back to the riverbed, passing
around a section of the river just below the impoundment.
It is undisputed that since 1935, Warren has needed a li
cense to operate the dams, currently within the authority of
the Federal Energy Regulatory Commission (FERC) under
the Federal Power Act. 16 U. S. C. §§ 817(1), 792; see also
Public Utility Act of 1935, § 210, 49 Stat. 846. FERC grants
these licenses for periods up to 50 years, 16 U. S. C. § 799,
Vermont, Darrell V. McGraw, Jr., of West Virginia, and Peggy S. Lauten
schlager of Wisconsin; for Friends of the Everglades by John E. Childe;
for Former Assistant Administrators of the United States Environmental
Protection Agency by Robert G. Dreher, Jennifer Chavez, and Howard I.
Fox; for the Hoopa Valley Tribe et al. by Thomas P. Schlosser, Carl Ull
man, and Daniel A. Raas; for the Miccosukee Tribe of Indians of Florida
by Dexter W. Lehtinen, Claudio Riedi, Sonia Escobio O’Donnell, and En
rique D. Arana; the National Wildlife Federation et al. by David K.
Mears; for Trout Unlimited et al. by James B. Dougherty; for Water Qual
ity and Riverine Scientists by Richard Roos-Collins and Steven P. Mal
loch; and for Senator James M. Jeffords by Mr. Jeffords, pro se.
Benjamin S. Sharp, Guy R. Martin, and Karen M. McGaffey filed a
brief for the Western Urban Water Coalition as amicus curiae.
†Justice Scalia joins all but Part III–C of this opinion.

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Opinion of the Court
after a review that looks to environmental issues as well as
the rising demand for power, § 797(e).
Over 30 years ago, Congress enacted a specific provision
for licensing an activity that could cause a “discharge” into
navigable waters; a license is conditioned on a certification
from the State in which the discharge may originate that it
will not violate certain water quality standards, including
those set by the State’s own laws. See Water Quality Im
provement Act of 1970, § 103, 84 Stat. 108. Today, this re
quirement can be found in § 401 of the Clean Water Act, 86
Stat. 877, 33 U. S. C. § 1341: “Any applicant for a Federal li
cense or permit to conduct any activity . . . which may result
in any discharge into the navigable water[s] shall provide the
licensing or permitting agency a certification from the State
in which the discharge originates . . . .” § 1341(a)(1).
“Any certification provided under this section shall set
forth any effluent limitations and other limitations, and
monitoring requirements necessary to assure that any
applicant for a Federal license or permit will comply
with [§§ 1311, 1312, 1316, and 1317] and with any other
appropriate requirement of State law set forth in such
certification, and shall become a condition on any Fed
eral license or permit subject to the provisions of this
section.” 1 § 1341(d).
In 1999, Warren sought to renew federal licenses for five
of its hydroelectric dams. It applied for water quality certi
fications from the Maine Department of Environmental Pro
1 The statutes cross-referenced go to effluent limitations and other limi
tations, 33 U. S. C. §§ 1311, 1312, standards of performance, § 1316, and
toxic effluent standards, § 1317. As we have explained before, “state
water quality standards adopted pursuant to § 303 [of the Clean Water
Act, 33 U. S. C. § 1313,] are among the ‘other limitations’ with which a
State may ensure compliance through the § 401 certification process.”
PUD No. 1 of Jefferson Cty. v. Washington Dept. of Ecology, 511 U. S.
700, 713 (1994).

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Opinion of the Court
tection (the state agency responsible for what have come to
be known as “401 state certifications”), but it filed its ap
plication under protest, claiming that its dams do not result
in any “discharge into” the river triggering application of
§ 401.
The Maine agency issued certifications that required
Warren to maintain a minimum stream flow in the bypassed
portions of the river and to allow passage for various migra
tory fish and eels. When FERC eventually licensed the five
dams, it did so subject to the Maine conditions, and Warren
continued to deny any need of § 401 state certification.
After appealing unsuccessfully to Maine’s administrative ap
peals tribunal, the Board of Environmental Protection, War
ren filed this suit in the State’s Cumberland County Superior
Court. That court rejected Warren’s argument that its
dams do not result in discharges, and the Supreme Judicial
Court of Maine affirmed. 2005 ME 27, 868 A. 2d 210. We
granted certiorari, 546 U. S. 933 (2005), and now affirm as
well.
II
The dispute turns on the meaning of the word “discharge,”
the key to the state certification requirement under § 401.2
The Act has no definition of the term, but provides that “[t]he
term ‘discharge’ when used without qualification includes a
discharge of a pollutant, and a discharge of pollutants.” 3 33
U. S. C. § 1362(16). It does define “discharge of a pollutant”
and “discharge of pollutants” as meaning “any addition of
any pollutant to navigable waters from any point source.”
2 No one disputes that the Presumpscot River is a navigable water of
the United States.
3 The term “pollutant” is defined in the Act to mean “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.” 33 U. S. C. § 1362(6).

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§ 1362(12). But “discharge” presumably is broader, else su
perfluous, and since it is neither defined in the statute nor a
term of art, we are left to construe it “in accordance with its
ordinary or natural meaning.” FDIC v. Meyer, 510 U. S.
471, 476 (1994).
When it applies to water, “discharge” commonly means
a “flowing or issuing out,” Webster’s New International
Dictionary 742 (2d ed. 1954); see also ibid. (“[t]o emit; to
give outlet to; to pour forth; as, the Hudson discharges its
waters into the bay”), and this ordinary sense has consist
ently been the meaning intended when this Court has used
the term in prior water cases. See, e. g., Marsh v. Oregon
Natural Resources Council, 490 U. S. 360, 364 (1989) (de
scribing a dam’s “ ‘multiport’ structure, which will permit
discharge of water from any of five levels”); Arizona v. Cali
fornia, 373 U. S. 546, 619, n. 25 (1963) (Harlan, J., dissenting
in part) (quoting congressional testimony regarding those
who “ ‘take . . . water out of the stream which has been dis
charged from the reservoir’ ”); United States v. Arizona, 295
U. S. 174, 181 (1935) (“Parker Dam will intercept waters dis
charged at Boulder Dam”).
In fact, this understanding of the word “discharge” was
accepted by all Members of the Court sitting in our only
other case focused on § 401 of the Clean Water Act, PUD
No. 1 of Jefferson Cty. v. Washington Dept. of Ecology, 511
U. S. 700 (1994). At issue in PUD No. 1 was the State of
Washington’s authority to impose minimum stream flow
rates on a hydroelectric dam, and in posing the question pre
sented, the Court said this:
“There is no dispute that petitioners were required to
obtain a certification from the State pursuant to § 401.
Petitioners concede that, at a minimum, the project will
result in two possible discharges—the release of
dredged and fill material during the construction of the
project, and the discharge of water at the end of the

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tailrace after the water has been used to generate elec
tricity.” Id., at 711.
The Pud No. 1 petitioners claimed that a state condition im
posing a stream flow requirement on discharges of water
from a dam exceeded the State’s § 401 authority to prevent
degradation of water quality, but neither the parties nor the
Court questioned that the “discharge of water” from the dam
was a discharge within the ambit of § 401. Ibid. And al
though the Court’s opinion made no mention of the dam as
adding anything to the water, the majority’s use of the
phrase “discharge of water” drew no criticism from the dis
sent, which specifically noted that “[t]he term ‘discharge’ is
not defined in the [Clean Water Act] but its plain and ordi
nary meaning suggests ‘a flowing or issuing out,’ or ‘some
thing that is emitted.’ ” Id., at 725 (opinion of Thomas, J.)
(quoting Webster’s Ninth New Collegiate Dictionary 360
(1991)).
In resort to common usage under § 401, this Court has not
been alone, for the Environmental Protection Agency (EPA)
and FERC have each regularly read “discharge” as having
its plain meaning and thus covering releases from hydroelec
tric dams. See, e. g., EPA, Water Quality Standards Hand
book § 7.6.3, p. 7–10 (2d ed. 1994) (“EPA has identified five
Federal permits and/or licenses that authorize activities that
may result in a discharge to the waters[, including] licenses
required for hydroelectric projects issued under the Federal
Power Act”); FPL Energy Maine Hydro LLC, 111 FERC
¶ 61,104, p. 61,505 (2005) (rejecting, in a recent adjudication,
the argument that Congress “used the term ‘discharge’ as
nothing more than a shorthand expression for ‘discharge of
a pollutant or pollutants’ ”).4 Warren is, of course, entirely
4 Warren relies on a document from the EPA as a counterexample of the
EPA’s position in this regard. See Memorandum from Ann R. Klee, EPA
General Counsel, et al., to Regional Administrators, regarding “Agency
Interpretation on Applicability of Section 402 of the Clean Water Act to

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correct in cautioning us that because neither the EPA nor
FERC has formally settled the definition, or even set out
agency reasoning, these expressions of agency understand
ing do not command deference from this Court. See
Gonzales v. Oregon, 546 U. S. 243, 258 (2006) (“Chevron def
erence . . . is not accorded merely because the statute
is ambiguous and an administrative official is involved”);
Skidmore v. Swift & Co., 323 U. S. 134, 140 (1944). But even
so, the administrative usage of “discharge” in this way con
firms our understanding of the everyday sense of the term.
III
Warren makes three principal arguments for reading the
term “discharge” differently from the ordinary way. We
find none availing.
A
The first involves an interpretive canon we think is out of
place here. The canon, noscitur a sociis, reminds us that
“a word is known by the company it keeps,” Gustafson v.
Alloyd Co., 513 U. S. 561, 575 (1995), and is invoked when a
string of statutory terms raises the implication that the
“words grouped in a list should be given related meaning,”
Dole v. Steelworkers, 494 U. S. 26, 36 (1990) (internal quota
tion marks omitted); see also Beecham v. United States, 511
U. S. 368, 371 (1994) (“That several items in a list share an
attribute counsels in favor of interpreting the other items as
possessing that attribute as well”).
Water Transfers” (Aug. 5, 2005), available at http://www.epa.gov/ogc/
documents/water_transfers.pdf (as visited Apr. 13, 2006, and available in
Clerk of Court’s case file). The memorandum does not help Warren, how
ever; it interprets § 402 of the Clean Water Act, not § 401, and construes
the statutory phrase “discharge of a pollutant,” which, as explained below,
implies a meaning different under the statute from the word “discharge”
used alone. The memorandum, in fact, declares that “[i]t does not address
any . . . terms under the statute other than ‘addition.’ ” Id., at 18.

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Warren claims that the canon applies to § 502(16) of the
Clean Water Act, which provides that “[t]he term ‘discharge’
when used without qualification includes a discharge of a pol
lutant, and a discharge of pollutants.” 33 U. S. C. § 1362(16).
Warren emphasizes that the “include[d]” terms, pollutant
discharges, are themselves defined to require an “addition”
of pollutants to water. § 1362(12). Since “discharge” pure
and simple is keeping company with “discharge” defined as
adding one or more pollutants, Warren says “discharge”
standing alone must require the addition of something for
eign to the water into which the discharge flows. And be
cause the release of water from the dams adds nothing to
the river that was not there above the dams, Warren con
cludes that water flowing out of the turbines cannot be a
discharge into the river.5
The problem with Warren’s argument is that it purports
to extrapolate a common feature from what amounts to a
single item (discharge of a pollutant plus the plural variant
involving more than one pollutant). See Beecham, supra, at
371. The argument seems to assume that pairing a broad
statutory term with a narrow one shrinks the broad one, but
there is no such general usage; giving one example does not
convert express inclusion into restrictive equation, and nos
citur a sociis is no help absent some sort of gathering with
5 We note that the Supreme Judicial Court of Maine accepted the asser
tion that “[a]n ‘addition’ is the fundamental characteristic of any dis
charge.” 2005 ME 27, ¶ 11, 868 A. 2d 210, 215. It then held that Warren’s
dams add to the Presumpscot River because the water “los[es its] status
as waters of the United States” when diverted from its natural course,
and becomes an addition to the waters of the United States when redepos
ited into the river. 868 A. 2d, at 216 (emphasis deleted). We disagree
that an addition is fundamental to any discharge, nor can we agree that
one can denationalize national waters by exerting private control over
them. Cf. United States v. Chandler-Dunbar Water Power Co., 229 U. S.
53, 69 (1913) (“[T]hat the running water in a great navigable stream is
capable of private ownership is inconceivable”). Thus, though we affirm
the Maine judgment, we do so on different reasoning.

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a common feature to extrapolate. It should also go without
saying that uncritical use of interpretive rules is especially
risky in making sense of a complicated statute like the Clean
Water Act, where technical definitions are worked out with
great effort in the legislative process. Cf. H. R. Rep. No.
92–911, p. 125 (1972) (“[I]t is extremely important to an un
derstanding of [§ 402] to know the definition of the various
terms used and a careful reading of the definitions . . . is
recommended. Of particular significance [are] the words
‘discharge of pollutants’ ”).
B
Regardless, Warren says the statute should, and even
must, be read its way, on the authority of South Fla. Water
Management Dist. v. Miccosukee Tribe, 541 U. S. 95 (2004).
But that case is not on point. Miccosukee addressed § 402
of the Clean Water Act, not § 401, and the two sections are
not interchangeable, as they serve different purposes and
use different language to reach them. Section 401 recast
pre-existing law and was meant to “continu[e] the authority
of the State . . . to act to deny a permit and thereby prevent
a Federal license or permit from issuing to a discharge
source within such State.” S. Rep. No. 92–414, p. 69 (1971).
Its terms have a broad reach, requiring state approval any
time a federally licensed activity “may” result in a discharge
(“discharge” of course being without any qualifiers here), 33
U. S. C. § 1341(a)(1), and its object comprehends maintaining
state water quality standards, see n. 1, supra.
Section 402 has a historical parallel with § 401, for the leg
islative record suggests that it, too, was enacted to con
solidate and ease the administration of some predecessor
regulatory schemes, see H. R. Rep. No. 92–911, at 124–125.
But it contrasts with § 401 in its more specific focus. It
establishes what Congress called the National Pollutant
Discharge Elimination System, requiring a permit for the
“discharge of any pollutant” into the navigable waters of the
United States, 33 U. S. C. § 1342(a). The triggering statu

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tory term here is not the word “discharge” alone, but “dis
charge of a pollutant,” a phrase made narrower by its speci
fic definition requiring an “addition” of a pollutant to the
water. § 1362(12).
The question in Miccosukee was whether a pump between
a canal and an impoundment produced a “discharge of a pol
lutant” within the meaning of § 402, see 541 U. S., at 102–103,
and the Court accepted the shared view of the parties that
if two identified volumes of water are “simply two parts of
the same water body, pumping water from one into the other
cannot constitute an ‘addition’ of pollutants,” id., at 109.
Miccosukee was thus concerned only with whether an “addi
tion” had been made (phosphorous being the substance in
issue) as required by the definition of the phrase “discharge
of a pollutant”; it did not matter under § 402 whether pump
ing the water produced a discharge without any addition.
In sum, the understanding that something must be added in
order to implicate § 402 does not explain what suffices for a
discharge under § 401.6
6 The fact that the parties in Miccosukee conceded that the water being
pumped was polluted does not transform the Court’s analysis from one
centered on the word “addition” to one centered on the word “discharge.”
Before Miccosukee, one could have argued that transferring polluted
water from a canal to a connected impoundment constituted an “addition.”
Miccosukee is at odds with that construction of the statute, but it says
nothing about whether the transfer of polluted water from the canal to
the impoundment constitutes a “discharge.”
Likewise, we are not persuaded by Warren’s claim that the word “into”
somehow changes the meaning of the word “discharge” so as to require an
addition. See Reply Brief for Petitioner 1–2 (“However one might read
the lone word ‘discharge’ by itself, the complete statutory phrase ‘dis
charge into the navigable waters’ entails the introduction of something
into the waters”). The force of this argument escapes us, since one can
easily refer to water being poured or discharged out of one place into
another without implying that an addition of some hitherto unencountered
mixture or quality of water is made. Indeed, the preposition “into” was
used without connoting an addition in the Miccosukee analogy cited by
Warren. See 541 U. S., at 110 (“[I]f one takes a ladle of soup from a

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C
Warren’s third argument for avoiding the common mean
ing of “discharge” relies on the Act’s legislative history, but
we think that if the history means anything it actually goes
against Warren’s position. Warren suggests that the word
“includes” in the definition of “discharge” should not be read
with any spacious connotation, because the word was simply
left on the books inadvertently after a failed attempt to deal
specifically with “thermal discharges.” As Warren de
scribes it, several Members of Congress recognized that
“heat is not as harmful as what most of us view as ‘pollut
ants,’ because it dissipates quickly in most bodies of receiv
ing waters,” 1 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. 273 (1973) (remarks of Rep.
Clark), and they proposed to regulate thermal discharges
less stringently than others. They offered an amendment to
exclude thermal discharges from the requirements under
§ 402, but they also wanted to ensure that thermal discharges
remained within the scope of § 401 and so sought to include
them expressly in the general provision covering “dis
charge.” See id., at 1069–1070, 1071. The proposed defini
tion read, “[t]he term ‘discharge’ when used without qualifi
cation includes a discharge of a pollutant, a discharge of
pollutants, and a thermal discharge.” Id., at 1071.
Of course, Congress omitted the reference to “thermal dis
charge,” and settled on the definition we have today. See
Federal Water Pollution Control Act Amendments of 1972,
§ 502(16), 86 Stat. 887. Warren reasons that once Congress
abandoned the special treatment for thermal pollutants, it
merely struck the words “thermal discharge” from 33
U. S. C. § 1362(16) and carelessly left in the word “includes.”
pot . . . and pours it back into the pot, one has not ‘added’ soup or anything
else to the pot” (internal quotation marks and brackets omitted)).

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Thus, Warren argues, there is no reason to assume that de
scribing “discharge” as including certain acts was meant to
extend the reach of § 401 beyond acts of the kind specifically
mentioned; 7 the terminology of § 401 simply reflects a failed
effort to narrow the scope of § 402.
This is what might be called a lawyer’s argument. We
will assume that Warren is entirely correct about the impe
tus behind the failed attempt to rework the scope of pollut
ant discharge under § 402. It is simply speculation, though,
to say that the word “includes” was left in the description of
a “discharge” by mere inattention, and for reasons given in
Part IV of this opinion it is implausible speculation at that.
But if we confine our view for a moment strictly to the draft
ing history, the one thing clear is that if Congress had left
“thermal discharge” as an included subclass of a “discharge”
under § 502(16), Warren would have a stronger noscitur a
sociis argument. For a thermal discharge adds something,
the pollutant heat, see n. 3, supra. Had the list of examples
of discharge been lengthened to include thermal discharges,
there would have been at least a short series with the com
mon feature of addition. As it stands, however, the only
thing the legislative history cited by Warren demonstrates
is the congressional rejection of language that would have
created a short series of terms with a common implication of
an addition.
Warren’s theory, moreover, has the unintended conse
quence of underscoring that Congress probably distin
guished the terms “discharge” and “discharge of pollutants”
deliberately, in order to use them in separate places and
to separate ends. Warren hypothesizes that Congress at
tempted to tinker with the definition of “discharge” because
it wanted to subject thermal discharges to the requirements
of § 401, but not § 402. But this assumption about Con
7 Warren is hesitant to follow its own logic to completion by simply
claiming that § 401 covers nothing but what § 502(16) mentions, the dis
charge of a pollutant or pollutants.

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gress’s motives only confirms the point that when Congress
fine-tunes its statutory definitions, it tends to do so with a
purpose in mind. See Bates v. United States, 522 U. S. 23,
29–30 (1997) (if “Congress includes particular language in
one section of a statute but omits it in another section of
the same Act, it is generally presumed that Congress acts
intentionally and purposely in the disparate inclusion or ex
clusion” (internal quotation marks omitted)).
IV
Warren’s arguments against reading the word “discharge”
in its common sense fail on their own terms.8 They also
miss the forest for the trees.
8 Warren briefly makes another argument for disregarding the plain
meaning of the word “discharge,” relying on § 511(c)(2) of the Clean Water
Act, 33 U. S. C. § 1371(c)(2). This section addresses the intersection of the
Act with another statute, the National Environmental Policy Act of 1969
(NEPA), 42 U. S. C. § 4321 et seq. NEPA “imposes only procedural re
quirements on federal agencies with a particular focus on requiring agen
cies to undertake analyses of the environmental impact of their proposals
and actions.” Department of Transportation v. Public Citizen, 541 U. S.
752, 756–757 (2004). Section 511(c)(2) makes the point that nothing in
NEPA authorizes any federal agency “authorized to license or permit the
conduct of any activity which may result in the discharge of a pollutant”
to review “any effluent limitation or other requirement established pur
suant to this chapter or the adequacy of any certification under [§ 401].”
33 U. S. C. § 1371(c)(2)(A). Warren argues that reading § 401 to cover
discharges generally would preclude duplicative NEPA review of certi
fications involving pollutant discharges, but allow such review of those
involving nonpollutant discharges.
But Warren overlooks the fact that “discharge of a pollutant” is used in
§ 511(c)(2) in the course of identifying the agency, not the activity to be
certified. Whether a § 401 certification involves an activity that dis
charges pollutants or one that simply discharges, FERC (as an agency
that may be described, always, as one with “author[ity] to license or permit
the conduct of any activity which may result in the discharge of a pollut
ant,” ibid.) may not review it. Thus, nothing in § 511(c)(2) is disturbed by
our holding that hydroelectric dams require § 401 state certifications. It
is still the case that, when a State has issued a certification covering a
discharge that adds no pollutant, no federal agency will be deemed to have

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Congress passed the Clean Water Act to “restore and
maintain the chemical, physical, and biological integrity of
the Nation’s waters,” 33 U. S. C. § 1251(a); see also PUD
No. 1, 511 U. S., at 714, the “national goal” being to achieve
“water quality which provides for the protection and propa
gation of fish, shellfish, and wildlife and provides for rec
reation in and on the water,” 33 U. S. C. § 1251(a)(2). To
do this, the Act does not stop at controlling the “addition
of pollutants,” but deals with “pollution” generally, see
§ 1251(b), which Congress defined to mean “the man-made or
man-induced alteration of the chemical, physical, biological,
and radiological integrity of water,” § 1362(19).
The alteration of water quality as thus defined is a risk
inherent in limiting river flow and releasing water through
turbines. Warren itself admits that its dams “can cause
changes in the movement, flow, and circulation of a river . . .
caus[ing] a river to absorb less oxygen and to be less pass
able by boaters and fish.” Brief for Petitioner 23. And sev
eral amici alert us to the chemical modification caused by
the dams, with “immediate impact on aquatic organisms,
which of course rely on dissolved oxygen in water to
breathe.” Brief for Trout Unlimited et al. as Amici Curiae
13; see also, e. g., Brief for National Wildlife Federation et al.
as Amici Curiae 6 (explaining that when air and water mix
in a turbine, nitrogen dissolves in the water and can be po
tentially lethal to fish). Then there are the findings of the
Maine Department of Environmental Protection that led to
this appeal:
“The record in this case demonstrates that Warren’s
dams have caused long stretches of the natural river bed
to be essentially dry and thus unavailable as habitat for
indigenous populations of fish and other aquatic organ
isms; that the dams have blocked the passage of eels
authority under NEPA to “review” any limitations or the adequacy of the
§ 401 certification.

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and sea-run fish to their natural spawning and nursery
waters; that the dams have eliminated the opportunity
for fishing in long stretches of river, and that the dams
have prevented recreational access to and use of the
river.” In re S. D. Warren Co., L–19713–33–E–N etc.
(2003), in App. to Pet. for Cert. A–49.
Changes in the river like these fall within a State’s legiti
mate legislative business, and the Clean Water Act provides
for a system that respects the States’ concerns. See 33
U. S. C. § 1251(b) (“It is the policy of the Congress to recog
nize, preserve, and protect the primary responsibilities and
rights of States to prevent, reduce, and eliminate pollution”);
§ 1256(a) (federal funds for state efforts to prevent pollution);
see also § 1370 (States may impose standards on the dis
charge of pollutants that are stricter than federal ones).
State certifications under § 401 are essential in the scheme
to preserve state authority to address the broad range of
pollution, as Senator Muskie explained on the floor when
what is now § 401 was first proposed:
“No polluter will be able to hide behind a Federal license
or permit as an excuse for a violation of water quality
standard[s]. No polluter will be able to make major in
vestments in facilities under a Federal license or permit
without providing assurance that the facility will comply
with water quality standards. No State water pollution
control agency will be confronted with a fait accompli by
an industry that has built a plant without consideration
of water quality requirements.” 116 Cong. Rec. 8984
(1970).
These are the very reasons that Congress provided the
States with power to enforce “any other appropriate require
ment of State law,” 33 U. S. C. § 1341(d), by imposing condi
tions on federal licenses for activities that may result in a
discharge, ibid.

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Reading § 401 to give “discharge” its common and ordinary
meaning preserves the state authority apparently intended.
The judgment of the Supreme Judicial Court of Maine is
therefore affirmed.
It is so ordered.