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Page Number: 26

20 

SACKETT v. EPA 

Opinion of the Court 

Dictionary 25; see Webster’s Third New International Dic-
tionary 26 (1976); see also Oxford American Dictionary & 
Thesaurus 16 (2d ed. 2009) (listing “adjoining” and “neigh-
boring” as synonyms of “adjacent”).  But “construing statu-
tory language is not merely an exercise in ascertaining ‘the
outer limits of a word’s definitional possibilities,’ ”  FCC v. 
AT&T Inc., 562 U. S. 397, 407 (2011) (alterations omitted), 
and  here,  “only  one  . . .  meanin[g]  produces  a  substantive 
effect that is compatible with the rest of the law,” United 
Sav. Assn. of Tex. v. Timbers of Inwood Forest Associates, 
Ltd., 484 U. S. 365, 371 (1988).  Wetlands that are separate
from  traditional  navigable  waters  cannot  be  considered 
part of those waters, even if they are located nearby.

In addition, it would be odd indeed if Congress had tucked
an important expansion to the reach of the CWA into con-
voluted language in a relatively obscure provision concern-
ing  state  permitting  programs.    We  have  often  remarked 
that Congress does not “hide elephants in mouseholes” by 
“alter[ing] the fundamental details of a regulatory scheme
in vague terms or ancillary provisions.”  Whitman v. Amer-
ican Trucking Assns., Inc., 531 U. S. 457, 468 (2001).  We 
cannot agree with such an implausible interpretation here. 
If §1344(g)(1) were read to mean that the CWA applies to 
wetlands  that  are  not  indistinguishably  part  of  otherwise 
covered “waters of the United States,” see supra, at 14, it 
would  effectively  amend  and  substantially  broaden 
§1362(7)  to  define  “navigable  waters”  as  “waters  of  the 
United  States  and  adjacent  wetlands.”  But  §1344(g)(1)’s
use of the term “including” makes clear that it does not pur-
port to do—and in fact, does not do—any such thing.  See 
National  Assn.  of  Home  Builders  v.  Defenders  of  Wildlife, 
551  U. S.  644,  662–664,  and  n. 8  (2007)  (recognizing  that
implied  amendments  require  “ ‘clear  and  manifest’ ”  evi-
dence of congressional intent).  It merely reflects Congress’s
assumption  that  certain  “adjacent”  wetlands  are  part  of 
“waters of the United States.”