                               In the

    United States Court of Appeals
                 For the Seventh Circuit
                     ____________________
No. 12-3800
STATE OF MICHIGAN, et al.,
                                                Plaintiffs-Appellants,

                                and

GRAND TRAVERSE BAND OF OTTAWA AND CHIPPEWA INDIANS,
                           Intervenor-Plaintiff-Appellant,

                                 v.

UNITED STATES ARMY CORPS OF ENGINEERS and
METROPOLITAN WATER RECLAMATION DISTRICT OF GREATER
CHICAGO,
                                Defendants-Appellees,

                                and

CITY OF CHICAGO, et al.,
                                 Intervenors-Defendants-Appellees.
                     ____________________

         Appeal from the United States District Court for the
           Northern District of Illinois, Eastern Division.
             No. 10 C 4457 — John J. Tharp, Jr., Judge.
                     ____________________

     ARGUED JANUARY 22, 2014 — DECIDED JULY 14, 2014
                ____________________
2                                                  No. 12-3800

   Before WOOD, Chief Judge, and MANION and WILLIAMS,
Circuit Judges.
    WOOD, Chief Judge. Meddling with Mother Nature is not
always a good idea, as the ongoing saga of the Asian carp
illustrates. The unfortunate confluence of two interven-
tions—the linkage of the Mississippi River system to the
Great Lakes and the effort to control weeds in southern
aquatic farms by importing Asian carp, a voracious non-
native fish—has led to a situation in which two particular
species of carp have overwhelmed the Mississippi River and
its tributaries and threaten to migrate into the Great Lakes.
Once the carp reach one of the Lakes, they have reached all
of them, thanks in part to the last Ice Age and in part to the
Erie Canal and later measures to facilitate shipping between
Lakes Huron and Erie and Lakes Erie and Ontario around
Niagara Falls. See, e.g., http://web2.geo.msu.edu/geogmich/
phy_feature.html (all websites cited in this opinion were last
visited on July 14, 2014). For an interesting account of the
construction of the Erie Canal and the Chicago Sanitary Ca-
nal, see Simon Winchester, THE MEN WHO UNITED THE STATES
at 196–222 (2013). Adding locks and canals to the natural
links between the Lakes opened the way for commercial
navigation all the way to the Atlantic Ocean. It is enough for
our purposes, however, to focus on the connections between
the Mississippi system and the Lakes.
   In this action, five states bordering the Great Lakes and
an Indian tribe assert that the Asian carp either will soon in-
vade, or perhaps already have invaded, the Great Lakes and
that they are poised to inflict billions of dollars of damage on
the ecosystem. Believing that the responsible units of gov-
ernment have failed in their task of protecting the Great
No. 12-3800                                                 3

Lakes, the plaintiffs ask us to step in and impose measures to
ensure that the carp are forever blocked from the Lakes.
    This problem did not develop overnight. Beginning in
the early 20th century, state and federal authorities con-
structed a series of canals and channels that connect Lake
Michigan with the Mississippi River. One part of that system
is now called the Chicago Area Waterway System (CAWS). It
has been vital to the growth and development of the Chicago
region and the surrounding Midwest. In addition to revers-
ing the flow of the Chicago River in order to carry Chicago’s
wastewater away from, rather than into, Lake Michigan, the
CAWS also established a navigable link between two of the
country’s most important bodies of water. The CAWS is not
the only place where the Mississippi basin and the Great
Lakes intersect, but it is the one at issue in our case.
    The other part of the problem dates from the 1970s, when
aquatic farmers in the southern United States introduced
bighead and silver Asian carp to their facilities in the hope
that the fish would control unwanted plant growth. See U.S.
Environmental Protection Agency, Asian Carp Species,
http://yosemite.epa.gov/r10/ECOCOMM.NSF/Invasive+Speci
es/Asian-Carp; National Park Service, Asian Carp Overview,
http://www.nps.gov/miss/naturescience/ascarpover.htm.
Flooding in the region, however, enabled the carp to move
beyond the farms out into open freshwater systems, and ul-
timately to work their way up the Mississippi River to with-
in six miles of Lake Michigan. See Fisheries and Oceans
Canada, Brief History of Asian Carp in North America and Re-
lated Initiatives in Canada, http://www.dfo-mpo.gc.ca/media/
back-fiche/2012/hq-ac15-eng.htm.
4                                                   No. 12-3800

    This is far from the first case in which neighboring states
have complained about one aspect or another of the CAWS.
Immediately after it was constructed, the State of Missouri
sued Illinois to stop operations of the Chicago Sanitary and
Ship Canal (a major component of the CAWS) because it
would cause sewage to flow down the Mississippi River and
into Missouri. See Missouri v. Illinois, 200 U.S. 496 (1906).
That suit was unsuccessful, but in later years interstate dis-
putes arose over the maximum rate at which Illinois could
divert water from Lake Michigan into the CAWS. See, e.g.,
Wisconsin v. Illinois, 449 U.S. 48 (1980); Wisconsin v. Illinois,
388 U.S. 426 (1967); Wisconsin v. Illinois, 311 U.S. 107 (1940);
Wisconsin v. Illinois, 278 U.S. 367 (1929). The case before us
presents yet another problem.
    In response to the advance of the Asian carp up to the
doorstep of the Great Lakes, the States of Michigan, Wiscon-
sin, Minnesota, and Ohio, and the Commonwealth of Penn-
sylvania, initiated this lawsuit against the U.S. Army Corps
of Engineers and the Metropolitan Water Reclamation Dis-
trict of Greater Chicago in an effort to compel action that
would prevent the fish from crossing into Lake Michigan.
The Grand Traverse Band of Ottawa and Chippewa Indians
intervened as a plaintiff. (For convenience, we refer to all
plaintiffs as the States, since the Tribe has associated itself
with all of the States’ arguments.) The States sought a pre-
liminary injunction that would require the Corps and the
District to take a number of aggressive interim measures to
maximize the chances of preventing the spread of the carp.
See Michigan v. U.S. Army Corps of Eng’rs (Asian Carp I), 667
F.3d 765 (2011). The district court denied that motion, and
we affirmed, holding that the States had failed to prove that
irreparable injury would occur before the litigation could be
No. 12-3800                                                    5

resolved, given the measures being undertaken by the re-
sponsible agencies.
    At that point proceedings resumed in the district court.
After further consideration, it dismissed the action under
Federal Rule of Civil Procedure 12(b)(6) for failure to state a
claim. The States have now appealed from that final judg-
ment. It is worth emphasizing that we give the plaintiffs the
benefit of the doubt in this situation: “We construe the com-
plaint in the light most favorable to the plaintiff, accepting as
true all well-pleaded facts alleged, and drawing all possible
inferences in [their] favor.” Tamayo v. Blagojevich, 526 F.3d
1074, 1081 (7th Cir. 2008). Any facts that we mention should
be understood in this light.
    Since we last saw this case, the threat that the Asian carp
pose to Lake Michigan has not diminished. As we did be-
fore, we proceed on the assumption that the risk of invasion
is a serious one, and that the negative consequences that
would result from the establishment of a breeding popula-
tion in the Great Lakes would be great. Nonetheless, while
our analysis differs in significant respects from that of the
district court, we ultimately agree with its disposition.
    We do not, in particular, adopt the district court’s conclu-
sion that the Corps and the District are “authorized” to op-
erate a navigable waterway no matter what the environmen-
tal cost, nor that any such authorization would relieve them
of the duty to try to stop the spread of the Asian carp. In-
stead, we find once again that the States have not alleged
facts showing that the Corps and the District are operating
the CAWS in a manner that is likely to allow the Asian carp
to reach Lake Michigan. As we did before, we leave open the
possibility of relief should there come a time when reliable
6                                                 No. 12-3800

facts show that the carp pose a more immediate threat to the
Lakes, or when the Corps and the District slacken their ef-
forts to prevent the passage of the Asian carp out into Lake
Michigan.
                                I
    The bighead and silver carp have not blended well with
the native species they have encountered. To the contrary,
the carp are rapacious eaters of plankton, algae, and other
small organisms. Over the years, they have crowded out the
native fish by destroying their food supply from the bottom
up, stripping the rivers of the key source of food for other
fish. (The carp are thus not apex predators that depend on
smaller fish for food.) A fish kill conducted near St. Louis in
1999 showed that the Asian carp constituted over 95% of the
biomass in the Mississippi at that place and time. See Great
Lakes Fishery Commission, testimony of Dr. Michael J. Han-
sen, “The Asian Carp Threat to the Great Lakes,” available at
http://www.glfc.org/fishmgmt/Hansen_testimony_aisancarp.
pdf.
    The carp are big fish: silver carp can reach up to 60
pounds and bighead carp up to 100 pounds, although the
average Asian carp weighs 30-40 pounds. Id. They can eat
between 20% and 120% of their own body weight daily. And
besides wreaking havoc on the Mississippi’s ecosystem, the
silver carp can be dangerous: when agitated (for example, by
motorboats), the carp leap out of the water, threatening
damage to recreational and commercial watercraft and inju-
ry to passengers on board.
   The Corps and the District have attempted for more than
a decade to address the growing threat to the Great Lakes
No. 12-3800                                                7

posed by the advance of the carp. In 2002, the Corps began
to operate a “Dispersal Barrier System,” which is a series of
electrically charged underwater cables meant to kill, shock,
or stun fish that try to pass by them. The first barrier was
built just north of the Lockport Lock and Dam in the CAWS.
It was joined by a second barrier 1300 feet downstream in
2009, and a third barrier between the two in 2011. See U.S.
Army        Corps     of    Engineers,    Electric  Barriers,
http://www.lrc.usace.army.mil/Missions/CivilWorksProjects/
ANSPortal/Barrier.aspx.
    In 2009, silver carp were spotted in the Chicago Sanitary
and Ship Canal, just south (away from the Lake) of the
Lockport Lock and Dam. In November of that year, “envi-
ronmental carp DNA” (eDNA), which is found by collecting
water samples and testing them for the presence of genetic
material emitted by the carp, was detected north (lakeward)
of the barrier system. (The reliability of eDNA was a matter
of some contention when we last considered this case, but
for present purposes we accept the States’ allegation that it
indicates immediate presence of the carp.) In response, the
Corps applied the fish poison rotenone near the barrier, and
a dead bighead carp was removed from the space north of
the Lockport Lock but south of the electrical barrier. The
Corps again applied rotenone in May 2010 in the Calumet-
Saganashkee (Cal-Sag) Channel, but it turned up no carp.
The following month, however, a single bighead carp was
recovered in Lake Calumet, well lakeward of the barrier and
only six miles from Lake Michigan.
    Since September 2010, the Asian Carp Regional Coordi-
nating Committee—a large group of federal and state agen-
cies (and some Canadian agencies) led by the White House
8                                                 No. 12-3800

Council on Environmental Quality—has regularly moni-
tored the CAWS for Asian carp and reported on its results.
See U.S. ARMY CORPS OF ENGINEERS, GREAT LAKES AND
MISSISSIPPI RIVER INTERBASIN STUDY REPORT (hereinafter
REPORT)       35     (Jan.    6,     2014),  available   at
http://glmris.anl.gov/documents/docs/glmrisreport/GLMRIS
_Report.pdf. Through April 2014, none of the Coordinating
Committee’s tests, which involve (among other things) a mix
of electrofishing and contracting with commercial fishing
crews, have discovered any bighead or silver carp lakeward
of the barriers. See Sampling Results, Asian Carp Regional
Coordinating Committee, http://www.asiancarp.us/sampling
/results.htm, and reports linked therein.
                              II
    Convinced that these efforts were inadequate to address
the problem, the States sued the Corps and the District in
2010; they named the Corps because it is responsible for
structures controlling navigation on the CAWS, and the Dis-
trict because it is responsible for the structures that control
water levels and water quality. The complaint raised claims
under both the federal common law of public nuisance and
the judicial review provisions of the Administrative Proce-
dure Act (APA), 5 U.S.C. § 702, although when we last saw
this case we noted that those claims were functionally the
same. See Asian Carp I, 667 F.3d at 787. The States seek a
permanent injunction requiring the Corps and the District to
take all appropriate and necessary measures expeditiously to
develop and implement plans to effect a hydrological sepa-
ration between Lake Michigan and the Mississippi River Ba-
sin—that is, to construct a physical barrier preventing any
water passage between them. They also wanted the court to
No. 12-3800                                                    9

order the Corps to expedite a congressionally mandated
study of options to prevent the spread of aquatic nuisance
species between the Great Lakes and the Mississippi River.
This study is known as the Great Lakes and Mississippi Riv-
er Interbasin Study Report; the parties all call it the
“GLMRIS Report,” but for simplicity we will refer to it simp-
ly as “the Report” unless the context requires otherwise. See
Water Resources Development Act of 2007, § 3062, Pub. L.
No. 110-114, 121 Stat. 1041 (2007).
    Worried that the threat of an Asian carp invasion is too
pressing to await these developments, the States additionally
sought a preliminary injunction requiring the Corps and the
District to take a host of interim steps, including (1) closing
all locks and sluice gates in the CAWS except as needed to
protect public safety; (2) installing temporary netting at stra-
tegic locations; and (3) applying rotenone on a regular basis.
The States’ appeal of the district court’s denial of that prelim-
inary relief led to our opinion upholding the district court’s
decision in 2011. See Asian Carp I, 667 F.3d 765. We conclud-
ed that the requested injunction was unlikely to reduce sig-
nificantly the risk that the carp would reach the Lake before
a trial on the merits could be completed. In so ruling, we
took into account both the substantial costs that such an in-
junction would impose on the region and the fact that the
Asian Carp Regional Coordinating Committee and its mem-
ber agencies are actively working to prevent the nuisance. Id.
at 789–90.
    We resolved several questions in Asian Carp I that remain
relevant to the current appeal. First, we held that sovereign
immunity did not bar this suit, as it falls within the waiver of
sovereign immunity found in the APA at 5 U.S.C. § 702. See
10                                                 No. 12-3800

Asian Carp I, 667 F.3d at 775–76. We also considered, without
deciding, the separate question whether a federal-common-
law public-nuisance claim can be stated against the federal
government. This question more appropriately related to
whether the States have stated a claim, we thought, and it
was not necessary to reach that issue in order to affirm the
denial of the requested preliminary injunction. Id. at 774. We
then addressed the question whether Congress had dis-
placed federal common law in this area by enacting statutes
addressing navigable waters and aquatic nuisance species.
Strictly speaking, we concluded, it had not. Id. at 777–79 (cit-
ing American Elec. Power Co. v. Connecticut, 131 S. Ct. 2527,
2537 (2011)). Nevertheless, we were unwilling to disregard
entirely the substantial efforts that the Corps and the District
(as well as the other involved agencies) are making. Even as-
suming that the States had demonstrated the necessary like-
lihood of success on the merits, we were not convinced that
the case for a preliminary injunction had been made. Asian
Carp I at 789. Not wanting to put the courts at cross-purposes
with the agencies already working to combat the advance of
the carp, we affirmed the denial of preliminary relief.
   On remand, the district court granted the joint motion of
the Corps and the District to dismiss the complaint for fail-
ure to state a claim upon which relief can be granted. See
FED. R. CIV. P. 12(b)(6). The court held that the defendants
could not have caused a public nuisance because “mainte-
nance of the hydrologic connection between CAWS and Lake
Michigan is not only lawful, it is also specifically authorized,
and in fact required, by statute.” It read the Rivers and Har-
bors Act, 33 U.S.C. § 401, to prevent the relief that the States
seek. That statute requires that construction of any “bridge,
causeway, dam, or dike” over any navigable body of water
No. 12-3800                                                 11

be approved by Congress, as well as by the Chief of Engi-
neers of the Corps and the Secretary of the Army. 33 U.S.C.
§ 401. Because congressional approval of a plan is required
before separation can be implemented, the court concluded,
“the Corps’ failure to effect that separation cannot be the
proximate cause of the alleged nuisance.” Although the
court granted the States leave to file an amended complaint,
they declined to do so. Accordingly, the court entered judg-
ment in favor of the defendants.
    Two intervening events have changed this case since we
last saw it. First, in 2012 Congress passed the Moving Ahead
for Progress in the 21st Century Act, Pub. L. No. 112-141, 126
Stat. 405 (2012) (hereinafter the “Progress Act”). Part of that
statute requires the Corps to expedite completion of the Re-
port—the one that the Corps originally had been ordered to
prepare in the Water Resources Development Act of 2007,
Pub. L. No. 110-114, 121 Stat. 1041 (2007). The Progress Act
directs the Corps to address the possibility of hydrological
separation and authorizes it to proceed “directly to precon-
struction engineering and design” if the Secretary of the Ar-
my determines that the completed study shows that a pro-
ject is justified. The statute imposed a February 6, 2014,
deadline to complete the report.
   The second development is the Corps’s completion of the
Report, which it released on January 6, 2014, two weeks be-
fore we heard oral argument. See SUMMARY OF THE GLMRIS
REPORT, available at http://glmris.anl.gov/documents/docs/
glmrisreport/GLMRISSummaryReport.pdf. The Report pre-
sents eight alternative plans for preventing the spread of
aquatic nuisance species between the Mississippi River Basin
and the Great Lakes Basin. Six of these plans, it predicts,
12                                                No. 12-3800

would stop the spread of the Asian carp within 25 years,
which happens to be the projected time for their arrival at
Lake Michigan. The Corps declined to make a recommenda-
tion among the alternatives. It took the position that “addi-
tional technical investigation, policy evaluation, NEPA [Na-
tional Environmental Policy Act] analysis, site-specific de-
tailed design, and public and state/agency reviews would
need to be accomplished prior to the recommendation of a
specific alternative.” Id. at ES-4.
    Two of the options identified in the Report—maintaining
the status quo and using only “nonstructural” measures
such as chemical control and netting—were projected to
have no impact on the spread of the carp. Of the six remain-
ing options, two involve complete hydrological separation of
the Mississippi from Lake Michigan (one calls for the use of
lakefront barriers; the other proposes barriers further away
from the Lake in the CAWS and the Cal-Sag Channel); two
involve partial hydrological separation but leave at least one
of the five current CAWS pathways open; and two do not
involve hydrological separation, but depend on additional
locks, barriers, and sluice gates (one of those adds a “buffer”
area between the controls where the Corps could respond to
aquatic nuisance threats). The “cheapest” of the options that
would prevent the spread of carp would require an estimat-
ed $7.806 billion to complete. The plans involving hydrologi-
cal separation are among the most expensive: the estimate
for lakefront hydrological separation is $18.389 billion, and
for mid-system separation $15.512 billion.
    The Report also considers the effect that each plan would
have first on the navigability, water quality, and ecosystems
of the CAWS and Lake Michigan, and second on the Dis-
No. 12-3800                                                  13

trict’s ability to control flooding. The Corps predicts that the
plans for hydrological separation would have a significant
negative impact on water quality in Lake Michigan in the
absence of additional curative measures; the plans would
also affect water quality and the ecosystem in the CAWS,
and they would prevent ships from moving from the Missis-
sippi River tributaries to Lake Michigan.
    We take judicial notice of the Report, as well as two other
reports offered by the States: one on the efficacy of the elec-
tric barriers currently in use, see U.S. Army Corps of Engi-
neers, Summary of Fish-Barge Interaction Research and Fixed
Dual Frequency Identification Sonar (DIDSON) Sampling at the
Electric Dispersal Barrier in Chicago Sanitary and Ship Canal,
http://www.lrc.usace.army.mil/Portals/36/docs/projects/ans/
docs/Fish-Barge%20Interaction%20and%20DIDSON%20at
%20electric%20barriers%20-%2012202013.pdf (DIDSON Re-
port), and the other on the potential for Asian carp reproduc-
tion in the Great Lakes Basin, see U.S. Geological Survey,
Hydraulic and Water-Quality Data Collection for the Investiga-
tion of Great Lakes Tributaries for Asian Carp Spawning and Egg-
Transport Suitability, USGS SCIENTIFIC INVESTIGATIONS REPORT
2013-5106, http://pubs.usgs.gov/sir/2013/5106 (Spawning
Report).
    When the Report was released, we asked the parties to be
prepared to discuss whether this case is now moot, in whole
or in part. The States emphatically state that it is not, and we
agree with them. Though they no longer need an order re-
quiring the Corps to expedite completion of the Report, a
number of important questions remain, including whether
the Corps must make a recommendation to Congress from
among the options laid out in the Report; whether only an
14                                                   No. 12-3800

option requiring hydrological separation will suffice; and
whether the Corps and the District must begin to work to-
ward hydrological separation.
                                 III
    This appeal takes us into the sometimes-murky area of
federal common law. Despite the pronouncement in Erie R.
Co. v. Tompkins, 304 U.S. 64, 78 (1938), that “[t]here is no fed-
eral general common law,” enclaves of federal common law
remain. One such enclave exists for cases dealing with “air
and water in their ambient or interstate aspects … .” Illinois
v. City of Milwaukee (Milwaukee I), 406 U.S. 91, 103 (1972). En-
vironmental protection is an area “‘within the national legis-
lative power’ … in which federal courts may fill in ‘statutory
interstices’ and, if necessary, even ‘fashion federal law.’”
American Elec. Power Co. v. Connecticut, 131 S. Ct. 2527, 2535
(2011) (quoting Henry J. Friendly, In Praise of Erie—And of the
New Federal Common Law, 39 N.Y.U. L. REV. 383, 421–22
(1964)). Federal courts look first to state law for this purpose,
and even when borrowing the law of a particular State
would be inappropriate, they are to remain mindful that
federal courts do not have creative power akin to that vested
in Congress. American Elec. Power, 131 S. Ct. at 2536. Federal
common law also can be displaced “when Congress ad-
dresses a question previously governed by a decision rested
on federal common law.” Id. at 2537 (quoting City of Milwau-
kee v. Illinois (Milwaukee II), 451 U.S 304, 314 (1981) (quotation
marks omitted)).
   A public nuisance is “an unreasonable interference with a
right common to the general public,” usually involving a
significant interference with public health, safety, peace,
comfort, or convenience. RESTATEMENT (SECOND) OF TORTS
No. 12-3800                                                   15

§ 821B. In Asian Carp I, we observed that this Restatement
definition “has been a common reference point for courts
considering cases arising under federal common law.” 667
F.3d at 780. Many types of conduct have been found to be a
public nuisance: for example, one state’s introduction of ty-
phoid into a river that runs off into another state, see Mis-
souri v. Illinois, 180 U.S. 208, 241–43 (1901); the discharge of
“noxious gas” from one state’s copper works into the other
state, see Georgia v. Tennessee Copper Co., 206 U.S. 230, 236
(1907); and changes to a state’s drainage system that cause
flooding in the farmland of another state, see North Dakota v.
Minnesota, 263 U.S. 365, 374 (1923). States may bring a feder-
al common law claim to vindicate not only their interests in
state property or property held in public trusts, but also in a
quasi-sovereign capacity to challenge activity “harmful to
their citizens’ health and welfare.” American Elec. Power, 131
S. Ct. at 2536. And “public nuisance law, like common law
generally, adapts to changing scientific and factual circum-
stances.” Id. (citing Missouri v. Illinois, 200 U.S. 496, 522
(1906)).
     Before we address whether the States have stated a pub-
lic nuisance claim, we must resolve a question we left open
in Asian Carp I: whether it is legally possible to state a public
nuisance claim against an agency of the federal government.
See 667 F.3d at 774. This is a different question from whether
the government enjoys sovereign immunity from such
claims. Sovereign immunity, when it exists, cuts off a plain-
tiff’s ability to sue the government. Here we are concerned
with the question whether the United States itself can create
a nuisance, or if the law adopts the fiction that any action
taken by the federal government is by definition in the pub-
16                                                 No. 12-3800

lic interest and therefore cannot be characterized as an un-
reasonable interference with a public right.
    As we explained in Asian Carp I, the term “public nui-
sance” originally described a criminal act of infringing on
the rights of the Crown. See id. at 773 (citing William L.
Prosser, Private Action for Public Nuisance, 52 VA. L. REV. 997,
998 (1966)). While we have left far behind such hoary doc-
trines as the Divine Right of Kings and the notion that the
Crown can do no wrong, the question remains whether it is
logically inconsistent to hold the federal government to ac-
count for a public nuisance. It is accepted that conduct “fully
authorized by statute, ordinance, or administrative regula-
tion” cannot subject an actor to liability for a public nui-
sance, see RESTATEMENT (SECOND) OF TORTS § 821B cmt. f. If
that is true, then how could action taken by the federal gov-
ernment endanger a public right? One might think that the
federal common law doctrine of public nuisance exists only
to create a uniform rule for resolving disputes between
states in a way that comports with the national interest. On
that view, the federal government is outside the scope of the
doctrine, because its actions are by definition in the national
interest.
    There is another perspective, however, and we find it
more persuasive. Federal public nuisance actions protect the
interests of the public against harms created by an actor’s
conduct that impinges on a public right. Whether such harm
is caused by a state or federal entity bears little relevance to
the doctrine’s purpose, which is to protect the endangered
right. And though the federal government is always at liber-
ty to define what constitutes an unreasonable interference
with a public right through legislation, the doctrine already
No. 12-3800                                                    17

accounts for this by contemplating displacement of federal
common law when Congress has spoken directly to the
question at issue. See American Elec. Power, 131 S. Ct. at 2537.
Indeed, the most that would happen if we were to accept the
idea that the government cannot create a public nuisance is
that the District would be sued alone, even though both enti-
ties have contributed to the same alleged infringement on a
public right. For reasons including the limited scope of their
delegated authority and the possibility of agency capture,
we have no interest in sustaining a fiction that executive
agencies’ undertakings so uniformly reflect the general in-
terest of the public that they should be impervious to public
nuisance liability. See, e.g., David Freeman Engstrom, Agen-
cies as Litigation Gatekeepers, 123 YALE L.J. 616, 663 (2013) (ex-
plaining general concerns about agencies’ abilities to act in
welfare-maximizing ways and avoid capture). We note as
well that the sweeping rule advocated by the Corps is incon-
sistent with the recognition in statutes including the APA
and the Federal Tort Claims Act, 28 U.S.C. § 1346(b), that the
United States might indeed act inconsistently with public
rights.
    Holding that federal agencies can be sued for creating a
public nuisance is consistent with the rule that actions au-
thorized by statute or regulation do not give rise to nuisance
liability. In this connection, it is important to distinguish be-
tween legislative and executive functions. When Congress
passes a statute, it weighs the competing public interests that
would be served. Activities commanded or authorized by
that statute reflect the public interest and so cannot be unrea-
sonable intrusions on a public right. Quasi-legislative agency
action is similar; agency rules promulgated pursuant to con-
gressional delegation enjoy the same presumption that they
18                                                 No. 12-3800

reflect the public interest. By contrast, agency action that re-
flects only the agency’s choice of a particular course of action
to implement a policy may or may not be consistent with the
underlying statute and regulations. The Restatement reflects
this distinction when it recognizes that a “statute, ordinance,
or administrative regulation” may authorize action, rather
than making the bolder assertion that any action taken by the
government cannot create a public nuisance. See
RESTATEMENT (SECOND) OF TORTS § 821B cmt. f.
    Federal agencies have appeared as defendants in public
nuisance suits before. In American Electric Power, the Tennes-
see Valley Authority was among the entities sued for causing
an alleged public nuisance with its substantial carbon diox-
ide emissions. See 131 S. Ct. at 2534. Middlesex County Sewer-
age Authority v. National Sea Clammers Association, 453 U.S. 1,
4 n.3 (1981), involved both the Environmental Protection
Agency and the Army Corps of Engineers. In both of those
cases the Supreme Court held that the suits could not pro-
ceed on other grounds, and so the Court had no occasion to
address the federal government’s appearance as a defendant.
It is hard to make much of this silence, but to the extent it
means anything, it suggests that the Court saw no sweeping,
easy-to-apply rule that would exempt the entire federal gov-
ernment, in all of its manifestations, from liability under the
federal common law of public nuisance. We conclude, in
summary, that the Corps can be held to account if liability
can otherwise be established, and we thus turn to the main
event: whether the States have stated a claim.
                                IV
    The district court, after determining that the only injunc-
tion that would satisfy the States would be one requiring the
No. 12-3800                                                 19

immediate hydrological separation of the Mississippi River
system from Lake Michigan by the placement of a perma-
nent barrier to navigation in the CAWS, held that they had
failed to state a public nuisance claim. It read the applicable
statutes not just to authorize, but to require, the defendants’
operation of the CAWS as a navigable waterway. The Corps
and the District amplify this argument before us, pointing to
a series of statutes that they claim add up to a congressional
mandate to keep the waterway open, no matter the cost.
    The defendants’ argument reaches back to the waterway’s
infancy. In a report on the initial allocation of federal funds
to the project, the Chief of Engineers wrote that the water-
way should provide “free public … navigation.” S. Doc. No.
71-126, at 5 (1930). Congress adopted the report’s recom-
mendations for the construction in the Rivers and Harbors
Act of 1930, 46 Stat. 918, which required the project to use
the smallest flow of water possible “in the development of a
commercially useful waterway.” Id. at 929. Later, in the Riv-
ers and Harbors Act of 1946, Congress adopted another re-
port of the Chief of Engineers that recommended construc-
tion of “a lock of suitable dimensions for barge navigation.”
H.R. Doc. No. 79-677, at 52 (1946) (emphasis added).
    This district court did not rely on these statutes, and for
good reason—they deal with construction specifications, not
with an “authorization” to run the CAWS in a way that
would allow an invasive species not yet introduced to the
United States to reach Lake Michigan more than half a cen-
tury later. The statutes reflect the obvious point that Con-
gress considered navigation when it funded construction of
structures on the CAWS, and that it accepted the Corps’s ad-
vice. As the States point out, the quote that defendants
20                                                No. 12-3800

culled from the Engineer’s Report that preceded the 1930 Act
was taken out of context. In isolation it could be read as an
expression of enduring policy, but in context it is apparent
that it was aimed at getting the state of Illinois to renounce
any future interest in blocking or charging fees on the wa-
terway. See S. Doc. No. 71-126 at 5.
     The district court also relied on two appropriations acts
from the early 1980s, as well as the original Rivers and Har-
bors Act (codified at 33 U.S.C. § 401), which forbids con-
struction of a dam in a navigable waterway without congres-
sional approval. In the Energy and Water Development Ap-
propriations Act of December 4, 1981, Pub. L. No. 97-88, 95
Stat. 1135, Congress provided that “[f]unds herein or herein-
after made available to the Corps of Engineers–Civil for op-
eration and maintenance of the Illinois Waterway shall be
available to operate and maintain the Chicago Sanitary and
Ship Canal portion of the Waterway in the interest of naviga-
tion.” The Supplemental Appropriations Act of July 30, 1983,
Pub. L. No. 98-63, 97 Stat. 301, clarified that the appropria-
tions provision in the 1981 Act “pertaining to maintenance
and operation of the Chicago Sanitary and Ship Canal of the
Illinois Waterway in the interest of navigation includes the
Control Structure and Lock in the Chicago River, and other
facilities as are necessary to sustain through navigation from
Chicago Harbor on Lake Michigan to Lockport on the Des
Plaines River.” The court thought that these appropriations
acts spelled out a “duty to operate and maintain the CAWS
in the interests of navigation.”
    But none of the statutes just mentioned requires the Corps
to keep the CAWS open for navigation at all times and under
all circumstances. Congress has expressed its intent that the
No. 12-3800                                                 21

CAWS be operated in the interest of navigation. When deci-
sions must be made, this implies, the Corps must try to facil-
itate navigation; that is all. Even the original Rivers and
Harbors Act cannot fairly be understood as a mandate to
force the waterway to remain open to navigation even if
there is an oil spill, or if the waters have become contaminat-
ed with some kind of noxious bacteria. That Act applies only
to the construction of new dams, and the Corps could pre-
vent all navigation in the CAWS without transgressing any
command in that statute simply by closing all of its existing
locks.
    Turning to the argument that keeping the waterway open
for navigation is “fully authorized,” the Corps and the Dis-
trict err by blurring the distinction between the actions they
are authorized to undertake and the possibly unlawful con-
sequences of their acts. We can assume that the statutes on
which they rely authorize them to create and maintain a
navigable waterway between the Mississippi River and Lake
Michigan. If the States’ complaint alleged that the existence
of a navigable waterway between the River and Lake was
itself a nuisance, their claim indeed would be foreclosed by
the “fully authorized” exception. But the States’ allegation is
not that a waterway qua waterway is a nuisance. Their claim
is that the nuisance arises because the Corps and the District
have together made it possible for the Asian carp to pass
from the Mississippi to the Great Lakes. Just as a speed limit
of 65 does not authorize a highway user to rear-end the
stopped car in front of her during a traffic jam, the authority
to run a navigable waterway does not authorize the Corps to
permit the passage of invasive species to a body of water
that would suffer severe adverse consequences as a result.
22                                                   No. 12-3800

   Some courts require that the specific action causing the
nuisance be unequivocally authorized by statute in order to
escape nuisance liability. See Varjabedian v. City of Madera, 572
P.2d 43, 47 (Cal. 1977). For example, even though an ordi-
nance might permit the construction of a sewage treatment
plant in a city, the foul odors emitted by the plant could still
constitute a nuisance for nearby homeowners. Id. at 46–47.
We need not decide whether federal common law demands
such a high degree of specificity to trigger the “fully author-
ized” exception. It is enough for present purposes that the
congressional legislation at issue does not even implicitly
touch on the problem of invasive species.
    The issue is muddled because the States drafted their
complaint with the ultimate goal of attaining hydrological
separation of the waterways. At some point, the Corps’s ina-
bility to effect hydrological separation on its own under the
Rivers and Harbors Act became confused with the Corps’s
authorization to cause an alleged nuisance. If, in an alternate
universe, the States were satisfied that something short of
hydrological separation would suffice to abate the nuisance
and the relief they requested would not significantly inter-
fere with navigation, it would be easy to see that the statutes
relied upon by defendants and the district court would not
“authorize” the agencies to allow the passage of Asian carp
to Lake Michigan. By the Corps’s own admission, there may
be methods of combating the carp’s advance that do not in-
volve hydrological separation; this is the premise of two of
the alternatives for combating aquatic nuisance species that
it lays out in the Report. See REPORT 103–33. The “fully au-
thorized” exception exempts a defendant from substantive
liability for its alleged nuisance; it does not affect the form of
relief after liability has been established. Once that is under-
No. 12-3800                                                   23

stood, it follows that the Corps’s duty to operate a navigable
waterway does not “fully authorize” it to create the nuisance
alleged in the States’ complaint.
                                 V
   The question remains whether any other ground in the
record supports the district court’s conclusion that the States’
complaint had to be dismissed under Rule 12(b)(6). Our re-
view is de novo, and so we now consider whether the facts
the States allege plausibly demonstrate that the defendants
are causing, or will cause, a public nuisance.
   Again, a public nuisance is a substantial and unreasona-
ble interference with a right common to the general public.
RESTATEMENT (SECOND) OF TORTS § 821B. For a number of
reasons, some of which we have just reviewed, the operation
of a manmade navigable waterway by itself is not a public
nuisance. The States recognize this: rather than asserting that
the CAWS itself is a public nuisance, they allege that the
manner in which defendants are operating the CAWS creates
a public nuisance. We look, therefore, at what the complaint
asserts on the latter point.
    The manner of operation involves more than the mainte-
nance of a manmade waterway between the Mississippi Riv-
er and Lake Michigan. It also involves the steps that the
Corps is taking and has already taken to prevent the carp
from passing through the CAWS to Lake Michigan, includ-
ing the presence of the electronic barriers, the regular moni-
toring activity, installation of screens on sluice gates, and the
application of rotenone when a potential threat is spotted.
The ongoing effort on the part of the Corps along with many
other actors to craft a plan to combat the eventual migration
24                                                 No. 12-3800

of the carp to Lake Michigan is yet another aspect of these
operations. The issuance of the Report was an important step
in that effort, and the Corps is committed to pursuing
whichever protective plan is selected. Even taking the States’
allegations as true, the defendants have been diligent in their
efforts to operate a waterway that blocks the passage of
Asian carp to Lake Michigan.
    At the time the complaint was filed, the States alleged
that an Asian carp had twice been discovered in areas lake-
ward of the electrical barriers—a bighead carp in December
2009 north of the Lockport Lock, and another bighead carp
in Lake Calumet in June 2010. The complaint also alleged
that carp eDNA was once discovered on the wrong side of
the Lockport Lock. The complaint noted that the Corps is
operating two electrical barriers to prevent fish passage
north of the Lockport Dam, and that it has applied rotenone
twice—once when it had to shut down an electrical barrier
for maintenance in December 2009, and again in May 2010
on a section of the Cal-Sag Channel.
     Since that time, the third barrier (Barrier IIB) has become
operational, and no new allegations of Asian carp appearing
in the CAWS have arisen. In the Report, the Corps predicts
that if no extra measures are taken, there is a “medium” risk
of Asian carp establishing themselves in the Great Lakes
within 25 years. (This apparently means that establishment
is likely but not certain, see REPORT 58.) The Corps believes
there is a low risk of invasion before that. See REPORT 192. In
addition, the States provided us with two reports. One, writ-
ten by the Corps, explains that barges may generate water
flow that pushes certain fish beyond the electrical barrier
(and that fish smaller than four inches may be able to swim
No. 12-3800                                                  25

through), but it disclaims any foreseeable threat from Asian
carp because of this. See DIDSON Report, supra at 13. The
other comes from the U.S. Geological Survey. It indicates that
tributary waters to the Great Lakes could serve as spawning
grounds for the carp (which need fast-flowing waters to
spawn in sufficient numbers to establish a sustainable popu-
lation). This indicates that the carp could establish them-
selves in the Great Lakes if they get that far. See Spawning
Report, supra at 13.
    In the final analysis, the States’ complaint does not plau-
sibly allege that the Corps and the District are creating a cur-
rent or imminent public nuisance by their manner of operat-
ing the CAWS. Even on the assumption (favorable to the
States) that the carp are advancing toward the CAWS and
will establish a sustainable population if they reach Lake
Michigan, none of the present allegations tends to show that
the Corps’s current method of operating the CAWS will
permit the Asian carp to pass. There is a notable lack of fac-
tual allegations that Asian carp are passing or are about to
pass the barriers that the Corps has established, and the
complaint does not plausibly allege that the Corps cannot or
will not respond to more urgent threats if and when they
arise. To the contrary, the allegations tend to show that the
Corps is taking its stewardship over the CAWS and the carp
problem seriously.
    We offer several final comments about this case. The
States’ complaint would require a court to direct the Corps to
work toward implementing one particular solution to the
threat of the Asian carp—hydrological separation. But we
know from the Report that the Corps is making diligent ef-
forts to find the solution best suited to accommodating the
26                                                No. 12-3800

competing concerns of stopping the passage of the fish and
preserving the publicly beneficial uses of the CAWS. A host
of competing concerns (water quality, navigation, public en-
joyment, cost) all must be weighed. We know also that there
is no quick fix here. Under these conditions, it would take an
unusually strong showing to meet the requirements for equi-
table relief. The complaint does not present facts that, if be-
lieved, would show that hydrological separation is the only
way to prevent the spread of the Asian carp. Cognizant of
our relative expertise as compared with that of the responsi-
ble executive agencies, we are reluctant to interfere with the
ongoing process to determine the best alternative for keep-
ing the Asian carp out of the Great Lakes.
    We do not want to be understood as taking this problem
lightly. We have proceeded throughout on the assumption
that the introduction of Asian carp to Lake Michigan would
pose a grave threat to the public’s use and enjoyment of the
Great Lakes. As we said in Asian Carp I, if new facts develop,
the States are free to return to court based on those changed
circumstances. Our decision pertains only to the complaint
that is before us.
    We also want to be careful that we are not misunder-
stood. The Corps and the District implied in their brief, and
again at oral argument, that they could not have “caused”
the nuisance because the fish are swimming lakeward of
their own accord, without any human intervention. We dis-
missed this argument at the preliminary injunction stage,
explaining that the defendants would “bear responsibility
for nuisances caused by their operation of a manmade wa-
terway between the Great Lakes and Mississippi water-
sheds.” Asian Carp I, 667 F.3d at 771. We reiterate that con-
No. 12-3800                                                  27

clusion today. Our decision does not depend on the fact that
the Asian carp are advancing upstream of their own volition.
It would be enough if the Corps and the District maintained
the CAWS in a way that allowed Asian carp to swim through
to Lake Michigan. It is the defendants’ apparent diligence,
rather than their claimed helplessness, that is key to our
holding today.
                               VI
    The district court also held that the States had not stated
a claim because they demanded relief that a federal court
could not provide. The States’ complaint makes clear their
belief that nothing short of hydrological separation will pre-
vent the spread of Asian carp from the Mississippi to the
Great Lakes. In that connection, we note that at first glance
the Rivers and Harbors Act seems to foreclose the possibility
of a court’s issuing an injunction requiring the Corps imme-
diately to build a structure separating the waterways. The
Act provides:
   It shall not be lawful to construct or commence the
   construction of any bridge, causeway, dam, or dike
   over or in any port, roadstead, haven, harbor, canal,
   navigable river, or other navigable water of the Unit-
   ed States until the consent of Congress to the building
   of such structures shall have been obtained and until
   the plans for … the dam or dike shall have been sub-
   mitted to and approved by the Chief of Engineers and
   Secretary of the Army.
33 U.S.C. § 401. The idea behind this portion of the Act was
to prevent unauthorized interference with navigation in in-
terstate or international waters, and so it makes sense to read
28                                                  No. 12-3800

the statute to cover the kind of hydrological barrier that the
States seek. Cf. Lake Shore & M.S. Ry. Co. v. Ohio, 165 U.S. 365,
369 (1897) (explaining purpose of the Act was to prevent
structures from “interfering with commerce”). A court could
not direct the Corps to build a dam in contravention of the
Act, because “[c]ourts of equity can no more disregard statu-
tory and constitutional requirements and provisions than
courts of law.” Hedges v. Dixon County, 150 U.S. 182, 192
(1893).
    That said, there is a subtle difference between what the
States want in practice and what they demand in this law-
suit. Perhaps with the Act in mind, their complaint is careful
not to ask for the barrier itself. Instead, they request an in-
junction requiring the Corps and the District to take “all ap-
propriate and necessary measures to expeditiously develop
and implement plans to permanently and physically sepa-
rate … [the waterways].” Such an injunction might require
the Corps by a specified deadline to choose among the alter-
natives in the Report for stopping the carp (and specifically
to choose one of the alternatives involving hydrological sep-
aration), and then promptly to seek congressional approval
to implement that plan. This position reflects the States’ be-
lief that absent some action by the Corps, Congress is unlike-
ly to solve this problem on its own. Congress appears to be
awaiting the Corps’s decision.
    An injunction requiring the Corps to exercise its discre-
tion in favor of a certain plan and essentially to lobby Con-
gress to adopt and provide funds for that plan, would be an
extraordinary and likely inappropriate use of a federal
court’s equitable powers. Drafting and enforcing such an in-
junction would be impracticable. See RESTATEMENT (SECOND)
No. 12-3800                                                  29

OF TORTS § 943 cmt. A; see also FED. R. CIV. P. 65 (d)(1)(C). It
also realistically might not provide any relief to the States,
because its effectiveness would depend entirely on the inde-
pendent workings of another branch of the federal govern-
ment.
    To the extent the States believe that the Corps has failed
to live up to its statutory duties, they may have other reme-
dies. They have argued that the Corps should have used the
Report to make recommendations as to which measures Con-
gress should adopt to combat the Asian carp, rather than of-
fering only alternative measures for stopping the carp’s pro-
gress. While they do not amplify on why they think that the
statute requires this, such an allegation (if properly pleaded)
could form the basis of a claim for judicial review of admin-
istrative action under 5 U.S.C. § 702 (particularly now that
the March 3, 2014, comment deadline for the Report has
passed and the Report has become a “final agency action”
for the purposes of review, see 5 U.S.C. § 704). Alternatively,
if the Corps stalls on progress toward a solution to the threat
of the Asian carp reaching the Great Lakes, there could come
a time when the States might be able to state a claim for re-
view of agency action “unlawfully withheld or unreasonably
delayed” within the meaning of 5 U.S.C. § 706(1). We express
no opinion as to the merits of these potential claims, which
are not before us.
    We conclude where we started. We accept for purposes of
this appeal that immeasurable environmental and economic
damage would be caused not only to Lake Michigan, but to
the Great Lakes as a whole, if the Asian carp establish breed-
ing populations there. But this point is uncontested, as the
active efforts of the Asian Carp Regional Coordinating
30                                                No. 12-3800

Committee demonstrate. The Corps and the District in par-
ticular are engaged in intensive efforts to prevent the carp
from reaching the Great Lakes, and there is a great deal of
evidence that indicates they have succeeded thus far in do-
ing so. Under these circumstances, we hold that the States
have failed to state a claim upon which relief can be granted,
either under a public nuisance theory or under the APA. We
therefore AFFIRM the judgment of the district court.
