                         PUBLISHED


UNITED STATES COURT OF APPEALS
              FOR THE FOURTH CIRCUIT


FRIENDS OF BACK BAY; BACK BAY            
RESTORATION FOUNDATION, LTD.,
                Plaintiffs-Appellants,
                  v.
UNITED STATES ARMY CORPS OF
ENGINEERS; JOHN MCHUGH, in his
official capacity as Secretary of
The Army; ROBERT L. VAN
ANTWERP, Lieutenant General, in             No. 11-1184
his official capacity as Chief of
Engineers and Commanding
General of the U.S. Army Corps
of Engineers; ANDREW W. BACKUS,
Colonel, in his official capacity as
District Engineer of the U.S.
Army Corps of Engineers, Norfolk
District,
               Defendants-Appellees.
                                         
        Appeal from the United States District Court
       for the Eastern District of Virginia, at Norfolk.
       Henry Coke Morgan, Jr., Senior District Judge.
                (2:10-cv-00270-HCM-TEM)

                  Argued: January 25, 2012

                   Decided: June 18, 2012

  Before KING, GREGORY, and FLOYD, Circuit Judges.
2          FRIENDS OF BACK BAY v. U.S. ARMY CORPS
Vacated and remanded by published opinion. Judge King
wrote the opinion, in which Judge Gregory and Judge Floyd
joined.


                         COUNSEL

ARGUED: Deborah M. Murray, SOUTHERN ENVIRON-
MENTAL LAW CENTER, Charlottesville, Virginia, for
Appellants. Brian C. Toth, UNITED STATES DEPART-
MENT OF JUSTICE, Washington, D.C., for Appellees. ON
BRIEF: Ignacia S. Moreno, Assistant Attorney General,
Environment & Natural Resources Division, Katherine J. Bar-
ton, UNITED STATES DEPARTMENT OF JUSTICE,
Washington, D.C., for Appellees.


                         OPINION

KING, Circuit Judge:

   Friends of Back Bay, together with Back Bay Restoration
Foundation, Ltd., the plaintiffs below, appeal the district
court’s award of summary judgment to defendants United
States Army Corps of Engineers (the "Corps"), Secretary of
the Army John McHugh, the Commanding General of the
Corps, Robert L. Van Antwerp, and Colonel Andrew W.
Backus, the District Engineer for the Corps in its Norfolk Dis-
trict. The plaintiffs’ Complaint challenged the Corps’s deci-
sion to approve a permit under section 404 of the Clean Water
Act ("CWA"), 33 U.S.C. § 1344, and section 10 of the Rivers
and Harbors Act of 1899 ("RHA"), 33 U.S.C. § 403, to build
a mooring facility and concrete boat ramp about 3,000 feet
from the Back Bay National Wildlife Refuge (the "Refuge")
in Virginia Beach, Virginia. As set forth below, we vacate the
district court’s judgment and remand.
             FRIENDS OF BACK BAY v. U.S. ARMY CORPS                      3
                                    I.

                                    A.

   Proposed by developer Kenneth Douglas Wilkins, the per-
mitted project (the "Project" or the "Wilkins Project") in a
man-made cove off North and Shipps Bays, tributaries to
Back Bay, would expand to 76 from 12 the number of exist-
ing slips at the same site, the additional 64 being dedicated for
watercraft use primarily by residents of nearby condomini-
ums. The approved permit directly authorizes channel dredg-
ing, as well as the excavation and relocation within the
Project area of silt and other material. See 33 U.S.C.
§ 1344(a) (empowering Secretary of the Army to "issue per-
mits . . . for the discharge of dredged or fill material into the
navigable waters [of the United States]"). In addition, the per-
mit provides for the construction of bulkheads, piers, mooring
piles, and a walkway in conjunction with the slips and ramp.
See 33 U.S.C. § 403 (requiring approval of Secretary for, inter
alia, "creation of any obstruction not affirmatively authorized
by Congress[ ] to the navigable capacity of any of the waters
of the United States").

   In mitigation of vegetated wetlands cleared to make way
for the facility, the permit specifies the creation of equivalent
wetlands nearby, and it requires the relocation there of the
plants being displaced by the new construction. The permit
also attaches a number of operational conditions to the com-
pleted Project, including horsepower limitations on boat
motors, restrictions on who may use the facility, and the
installation of signs informing the public of the establishment
of a no-wake zone (the "NWZ") for watercraft within the Ref-
uge. See J.A. 232-33.1
  1
   Citations herein to "J.A. ___" refer to the contents of the Joint Appen-
dix filed by the parties to this appeal.
4            FRIENDS OF BACK BAY v. U.S. ARMY CORPS
   Prior to issuing the permit, the Corps solicited public com-
ment on the underlying application; it received over 350
responses, "the overwhelming majority of which were in
opposition to the project." J.A. 194. The mayor of Virginia
Beach recounted that various state and federal government
agencies had "expended countless millions of dollars to con-
serve Back Bay," and she expressed concern that "detrimental
environmental impacts" would result from "greatly
increase[d] access for jet skis and powerboats" to the ecologi-
cally sensitive area. J.A. 152-53.

   In considerably more detail, the Gloucester, Virginia, field
office of the United States Fish and Wildlife Service (the
"FWS") documented the historical efforts to preserve and
restore submerged aquatic vegetation ("SAV") in the area.
The FWS surmised that "well documented" adverse effects of
motorized watercraft, such as "sediment resuspension, water
pollution, shoreline erosion, destruction of SAV and other
wetlands, and disturbance to fish and wildlife," would
increase if the Wilkins Project were fully realized, and pre-
dicted that "because Back Bay is a shallow water system,
these effects are likely to be amplified." Id. at 159.2 The
Regional Director of the FWS followed up with a separate
comment, in which he maintained that the § 404 discharges
occasioned by the Project "will have a substantial and unac-
ceptable impact on aquatic resources of national importance,"
and that, consequently, "the subject permit must be modified,
conditioned, or denied." Id. at 166.
    2
   The FWS pointed out that a nearby Corps district headquartered in
Wilmington, North Carolina, "is working with many other State and Fed-
eral partners in a joint effort to improve the aquatic and wetlands environ-
ments" in Back Bay and adjacent Currituck Sound (straddling Virginia
and North Carolina), opining that "issuance of a permit for this type of
facility . . . will open the door for additional development that is not com-
patible with the watershed restoration goals developed by many agencies
and partners for the Back Bay estuary." J.A. 158, 160.
           FRIENDS OF BACK BAY v. U.S. ARMY CORPS            5
   Similar sentiments were echoed by the Virginia Depart-
ment of Game and Inland Fisheries (warning that "restoration
efforts will face even more challenges in this unique system
and may ultimately be rendered unsuccessful"), J.A. 168, and
the federal Environmental Protection Agency (professing its
belief that "the proposed project is contradictory to the envi-
ronmental goals of several federal, state, [and] local resource
agencies and the public interests," and thus "strongly recom-
mends that the Corps deny the applicant’s request for per-
mits"), id. at 165. The FWS likewise supported "denial of this
project as proposed," id. at 161, but suggested that if the
Corps were inclined to proceed, it should prepare an Environ-
mental Impact Statement ("EIS") to address "impacts to Fed-
eral trust resources . . . due to project construction and
operation, habitat loss, and disruption/elimination of migra-
tory pathways and feeding and resting areas." Id. at 160-61.

   An EIS is "a detailed statement" that ascertains, among
other things, the effect of the proposed action on the environ-
ment, including "any adverse environmental effects which
cannot be avoided should the proposal be implemented," and
evaluates alternatives. 42 U.S.C. § 4332(2)(C). As an integral
underpinning of the National Environmental Protection Act
("NEPA"), an EIS must be devised in connection with "every
recommendation or report on proposals for . . . major Federal
actions significantly affecting the quality of the human envi-
ronment." Id.; see State ex rel. Campbell v. O’Leary, 64 F.3d
892, 896 (4th Cir. 1995). To determine whether a particular
action meets the threshold of "significantly affecting" envi-
ronmental quality, federal agencies are required to draft an
Environmental Assessment ("EA"), which is "a concise public
document" designed to "provide sufficient evidence and anal-
ysis for determining whether to prepare an [EIS] or a finding
of no significant impact [‘FONSI’]." 40 C.F.R.
§ 1508.9(a)(1); see Campbell, 64 F.3d at 896.

   In its March 1, 2005 Public Notice of the permit applica-
tion, the Corps announced its preliminary determination "that
6            FRIENDS OF BACK BAY v. U.S. ARMY CORPS
. . . no [EIS] will be required." J.A. 150. In light of the FWS
comments advocating for denial or, at a minimum, urging
preparation of an EIS, the Corps broached the concept of the
NWZ, which it could create through designating the Project
vicinity a Temporary Restricted Area.3 An internal memoran-
dum dated June 16, 2006, reflected the Corps’s understanding
that the FWS "indicated that implementation of the [NWZ]
regulation should alleviate many of their concerns and that
they will likely withdraw their objection to the Wilkins [Proj-
ect] once this plan is in effect." Id. at 195.

   The NWZ went into effect that same day by virtue of a
Local Order, for which Public Notice was subsequently pro-
vided on June 28, 2006. Therein, the Corps recognized that
watercraft use in and around the Refuge was "adversely
impacting [SAV] and nesting, feeding and breeding birds as
well as causing shoreline erosion from boat wakes." Id. at
197. According to the Corps, the NWZ would secure "a sig-
nificant measure of protection to the Refuge and its
resources." Id. The Local Order expired on December 31,
2007, after which the Corps made permanent the Restricted
Area designation, effective May 16, 2008. The official Corps
Memoranda issued in connection with the temporary and per-
manent designations each provided that the NWZ

     may be enforced by any Federal Agency, State,
   3
     The Corps’s regulations explain that a "restricted area" is "[a] defined
water area for the purpose of prohibiting or limiting public access to the
area. Restricted areas generally provide security for Government property
and/or protection to the public from the risks of damage or injury arising
from the Government’s use of that area." 33 C.F.R. § 334.2(b). A "no-
wake zone" is not specifically defined, but within the context of the per-
manent Restricted Area designation, detailed infra, the NWZ in this case
means that, save for certain carefully delineated exceptions, "[n]o vessel
of any type shall operate at a speed that causes a wake while they are
within 100 yards of the shoreline of the Back Bay National Wildlife Ref-
uge." J.A. 211. The shoreline is deemed to commence at the "Ordinary
High Water" mark. Id.
           FRIENDS OF BACK BAY v. U.S. ARMY CORPS            7
    Local or County Law Enforcement agency, or Pri-
    vate Security Firms in the employment of the
    [Corps] or U.S. Fish and Wildlife Service so long as
    the entity undertaking enforcement action has the
    legal authority to do so under the appropriate Fed-
    eral, State, or Local laws.

Id. at 192, 212.

   As a practical matter, however, enforcement of the NWZ
appears to be problematic. In the course of interagency dis-
cussions of the Project in 2006, it was revealed that the
marine detachment of the Virginia Beach Police Department
was "unable to routinely patrol the Back Bay due to current
staffing constraints." J.A. 186. Responding to the continuing
concerns expressed by the FWS, Colonel Dionysios Anninos,
the District Commander for the Corps, conceded on Septem-
ber 11, 2008, that "[e]nforcement will be an issue," but he was
"hopeful" that compliance with the NWZ would be achieved
"through education, signage, [and] public pressure." Id. at
203, 223. Colonel Anninos insisted, however, that "the lack
of funding necessary for a state or federal agency to fulfill
obligations is not a sufficient reason to deny a project." Id.

   By letter of October 3, 2008, the FWS Regional Office
memorialized the agency’s ongoing discussions with the
Corps concerning the Wilkins Project. Although the FWS
acknowledged that "details of the measures are still to be
worked out," its acquiescence in the Project was conditioned
on "[a]dequate funding for the enforcement of" the NWZ,
with further discussions to be conducted as to the proper allo-
cation of "[r]esponsibility of enforcement and cost share
funds." J.A. 226-27. On October 10, 2008, Colonel Anninos
wrote to his district’s regulatory section, explaining that the
Corps’s coordination with the FWS had addressed the latter
agency’s concerns. See id. at 229. That same date, the Corps
issued the permit.
8          FRIENDS OF BACK BAY v. U.S. ARMY CORPS
   The permit, however, neither mandates enforcement of the
NWZ nor guarantees funding therefor. Aside from requiring
that signage be posted, the permit specifies only that Wilkins
"serve on and participate in a committee of local, state and
federal agencies and community stakeholders to attempt to
establish a funding program for enforcement of the [NWZ] in
Back Bay." J.A. 233. The permit identifies several potential
sources for such funding, including grants, assessments, and
user fees, and notes that Wilkins also "may be required to
contribute a fair and equitable portion of the funding for this
program." Id. at 234.

   In the final EA, issued contemporaneously with the permit,
Colonel Anninos, on behalf of the Corps, reiterated the "con-
sensus . . . that the currently unrestricted use of the waters in
and around the Refuge may be having an adverse impact on
the sensitive and unique natural resources of the . . . Refuge
and Back Bay as a whole." J.A. 259. The Corps observed,
however, that refusing the permit "would not solve existing
and future problems associated with recreational boating in
Back Bay," and insisted that "denying this proposal would
logically necessitate the denial of all future private piers, boat
ramps and mooring projects in Back Bay due to the potential
for cumulative impacts." Id. at 269. Notwithstanding that
"there are no city or state maritime patrols within the Bay,"
id. at 261, the Corps asserted that the NWZ "will limit and
reduce any adverse impacts from the construction and opera-
tion of the facility," id. at 250. The EA culminated in a
FONSI, thus declaring that "no [EIS] will be prepared." Id. at
277.

                               B.

   The plaintiffs filed a Complaint in the District Court for the
District of Columbia on December 14, 2009, seeking review
of the Corps’s decision, in accordance with § 404 of the
CWA, to allow the dredging and subsequent discharge via
relocation of silt and fill material, and challenging the Corps’s
           FRIENDS OF BACK BAY v. U.S. ARMY CORPS                9
determination that issuance of the permit does not qualify
under NEPA as a federal action "significantly affecting the
quality of the human environment," such that an EIS must be
prepared in advance. On the defendants’ motion, and over the
plaintiffs’ opposition, venue was subsequently transferred to
the Eastern District of Virginia.

   The district court exercised jurisdiction over both aspects of
the Complaint pursuant to the general review provisions of
the Administrative Procedure Act ("APA"). See 5 U.S.C.
§§ 702, 704; Ohio Valley Envtl. Coal. v. Aracoma Coal Co.,
556 F.3d 177, 192 (4th Cir. 2009) (instructing that "[c]laims
challenging federal agency action under the CWA and NEPA
are subject to judicial review under the APA"). The court
directed the filing of the administrative record, after which the
parties submitted cross-motions for summary judgment. Fol-
lowing a hearing on January 28, 2011, the district court, by its
Opinion and Order of February 9, 2011, entered judgment on
behalf of the defendants.

   In so doing, the district court rejected the plaintiffs’ conten-
tion that potential harm to the Refuge from boating activities
could properly be considered a legitimate secondary effect of
the dredging and filling authorized pursuant to the CWA. See
Friends of Back Bay v. U.S. Army Corps of Eng’rs, No. 2:10-
cv-0070, slip op. at 36 (E.D. Va. Feb. 9, 2011). With respect
to the NEPA challenge, the court concluded that the Corps’s
decision to grant the permit without preparing an EIS was
within the agency’s broad discretion and not contrary to law.
See id. at 30. Upon timely notice filed on February 23, 2011,
the plaintiffs pursue this appeal.

                                II.

   The APA provides that a reviewing court is bound to "hold
unlawful and set aside agency action" for certain specified
reasons, including whenever the challenged act is "arbitrary,
capricious, an abuse of discretion, or otherwise not in accor-
10         FRIENDS OF BACK BAY v. U.S. ARMY CORPS
dance with law." 5 U.S.C. § 706(2)(A); see Ohio Valley Envtl.
Coal. v. Aracoma Coal Co., 556 F.3d 177, 192 (4th Cir.
2009). The foregoing statutory criteria render our oversight
"highly deferential, with a presumption in favor of finding the
agency action valid," yet the arbitrary-and-capricious standard
does not "reduce judicial review to a rubber stamp of agency
action." Id. (citation and internal quotation marks omitted).

   To comply with NEPA, "federal agencies must take a ‘hard
look’ at the potential environmental consequences of their
actions." Aracoma Coal, 556 F.3d at 191 (citation omitted).
In a similar fashion, we must "engage in a ‘searching and
careful’ inquiry of the record," so that we may "consider
whether the agency considered the relevant factors and
whether a clear error of judgment was made." Id. at 192
(quoting Citizens To Preserve Overton Park, Inc. v. Volpe,
401 U.S. 402, 416 (1971)). Insofar as an agency’s decision
may be deemed unreasonable as a matter of law, it is likely
to have been arbitrary and capricious. See Marsh v. Oregon
Natural Res. Council, 490 U.S. 360, 377 n.23 (1989) (noting
courts’ adoption of "arbitrary and capricious" and "reason-
ableness" standards under the APA, and explaining that dif-
ference between the two "is not of great pragmatic
consequence"). We evaluate the reasonableness of the Corps’s
decisionmaking de novo, without deference to the district
court’s resolution of the issue. See Hughes River Watershed
Conservancy v. Glickman, 81 F.3d 437, 443 (4th Cir. 1996).

                             III.

                              A.

                              1.

   The parties devoted much effort below, and have again on
appeal, debating how to properly characterize the EA.
According to the plaintiffs, the Corps found at the threshold
that granting the permit would affect the environment to the
           FRIENDS OF BACK BAY v. U.S. ARMY CORPS             11
degree necessary to trigger the need for an EIS, but that estab-
lishment of the NWZ would ameliorate the adverse effects
such that the net result would be no significant impact. When
an agency relies on such a "mitigated FONSI," it may avoid
preparing an EIS. See Ohio Valley Envtl. Coal. v. Aracoma
Coal Co., 556 F.3d 177, 191-92 (4th Cir. 2009). In support of
their position, the plaintiffs point out that the permit applica-
tion caused the Corps to examine and appreciate the problems
associated with watercraft use in Back Bay; the Project thus
spurred the Corps’s decision to designate the Refuge as a
Restricted Area and impose the NWZ.

   The defendants, to the contrary, maintain that because the
NWZ was in effect for nearly two years prior to issuance of
the EA, it constituted a "baseline" condition reflecting the
state of the environment absent any undertaking pursuant to
the permit. See N.C. Wildlife Fed’n v. N.C. Dep’t of Transp.,
No. 11-2210, 2012 WL 1548685 (4th Cir. May 3, 2012), at *6
(equating baseline with "no action" EIS alternative mandated
for consideration by 40 C.F.R. § 1502.14(d)). As such, the
argument goes, the Corps considered from a historical per-
spective (albeit a somewhat brief one) the issues giving rise
to its creation of the Restricted Area and the efficacy of the
NWZ in resolving those issues, but nonetheless concluded
that a FONSI was appropriate.

   The parties perceive the mitigation/baseline distinction
important in light of pertinent authorities requiring that
assumptions underlying a mitigated FONSI be supported by
record evidence. See, e.g., Hill v. Boy, 144 F.3d 1446, 1450-
51 (11th Cir. 1998) (ruling Corps’s refusal to prepare EIS
arbitrary and capricious where no evidence supported key
mitigation assumption and no analysis conducted gauging
effect of opposite assumption); Nat’l Audubon Soc’y v. Hoff-
man, 132 F.3d 7, 17 (2d. Cir. 1997) (concluding that Forest
Service arbitrarily and capriciously bypassed EIS where
record failed to establish likely efficacy of mitigation pro-
posal). An unjustified leap of logic or unwarranted assump-
12           FRIENDS OF BACK BAY v. U.S. ARMY CORPS
tion, however, can erode any pillar underpinning an agency
action, whether constructed from the what-is or the what-
may-be. Once the roof caves in, it offers but a smattering of
solace to explain that only the latter were inspected and
deemed sound.

   A material misapprehension of the baseline conditions
existing in advance of an agency action can lay the ground-
work for an arbitrary and capricious decision. We recently
confronted precisely that situation in North Carolina Wildlife
Federation, supra. There, the federal and state agencies
charged with evaluating the construction of a proposed toll
highway erroneously adopted the assumption that the road
would be built in estimating the consequences resulting from
no action being taken. In light of the obvious and fundamental
blunder, we had no difficulty remanding the matter for recon-
sideration, noting that "courts not infrequently find NEPA
violations when an agency miscalculates the ‘no build’ base-
line or when the baseline assumes the existence of a proposed
project." N.C. Wildlife Fed’n, 2012 WL 1548685, at *6 (cita-
tions and footnote omitted).

   Here, it cannot be disputed that the creation and continued
existence of the NWZ is a foundational proposition upon
which the FONSI was premised. The EA did not pretend to
the contrary; the Corps, to its credit, did not endeavor therein
to downplay the potential deleterious consequences if water-
craft are suffered to freely scurry about the Refuge.4 The
  4
   The EA asserts that educating the public about the NWZ, as an integral
part of the operational conditions incorporated within the permit and made
an enforceable condition thereof, "will ensure that boaters from the Wil-
kins . . . Facility will not adversely impact the ecologically sensitive Back
Bay/North Bay area," and "will limit and reduce any adverse impacts from
the construction and operation of the facility." J.A. 250. In summing up
the EA, Colonel Anninos expressed the Corps’s conclusion that the permit
conditions were of sufficient heft such that "there are no longer substantial
adverse impacts" associated with the Project. J.A. 277. The defendants
contend that "adverse impacts" and even "substantial adverse impacts" do
             FRIENDS OF BACK BAY v. U.S. ARMY CORPS                       13
NWZ, however, is entirely unenforced. Indeed, as revealed at
the hearing below on January 28, 2011, the NWZ remained
unmarked and undisclosed to the public nearly five years after
its initial implementation. See J.A. 63, 73-74. As the district
court astutely remarked at the hearing, "[E]ven if people
wanted to obey the no wake zone, I don’t know how in the
world they could do it without it being marked." J.A. 78.

   The most that the Corps could say was that it was "hopeful"
that the public would comply with the secret NWZ. J.A. 203,
223. No doubt the thoughtful folks who leave cauldrons of
candy on their front porches at Halloween hope the neighbor-
hood trick-or-treaters will behave themselves and take only
their fair share, but common experience has shown that those
hopes often remain unfulfilled. While the betrayal of trust on
All Hallows’ Eve might cost the credulous a bag or two of
sweets, the potential cost to the Refuge in this case from the
Corps’s hopefulness is, inarguably, considerably higher.

   Measures designed to render minimal a particular action’s
impact upon the environment, whether proposed in mitigation
or assumed to already exist, are more readily deemed effica-
cious (and thus more comfortably within an agency’s broad
prerogative to propose or assume) "when they are likely to be
policed," Hoffman, 132 F.3d at 17 (citing Abenaki Nation of
Mississquoi v. Hughes, 805 F. Supp. 234, 239 n.9 (D. Vt.

not necessarily rise to the level of "significant impacts" triggering an EIS,
but any notion that unrestricted watercraft access to the Refuge would be
of no significance under NEPA is belied both by the lack of that sort of
analysis in the EA and by the sustained efforts of the Corps in pursuing
and implementing the temporary Local Order and subsequent Restricted
Area designation. The Corps undertook both courses of conduct notwith-
standing its estimate that the 64 additional slips associated with the Wil-
kins Project would increase traffic no more than three to six percent, see
J.A. 257, and despite a three-day stakeout of about ten percent of the Ref-
uge it conducted in August 2006, at the conclusion of which the Corps sur-
mised that there is "minimal traffic on the bay during the majority of the
boating season." J.A. 260.
14         FRIENDS OF BACK BAY v. U.S. ARMY CORPS
1992)). Such policing may occur prospectively by administra-
tive enforcement through the imposition of a mandatory per-
mit condition, as in Abenaki Nation, or it may be recognized
as a baseline incident, enforced by a literal police presence.
Neither is currently the case in Back Bay.

   Absent any reasonable basis to conclude that, as of October
2008, the NWZ was being adequately enforced or its efficacy
was otherwise assured, the concept thereof as discussed
within the EA was a logical nullity. Being unable to divorce
the Corps’s demonstrably incorrect assumption of an effective
NWZ from its ultimate conclusion that no EIS need be pre-
pared, we find ourselves constrained to invalidate the resul-
tant FONSI as arbitrary and capricious. The judgment below
to the contrary must therefore be vacated, and the matter
remanded to the district court for further remand to the Corps.

                                2.

   The question remains as to what action the Corps may take
on remand. The Council on Environmental Quality has pro-
mulgated a regulation intended to guide federal agencies in
ascertaining the likelihood that their actions will, within the
meaning of NEPA, significantly affect the environment. See
40 C.F.R. § 1508.27. Decisionmakers are required to consider
both context and intensity, with the latter criterion "refer[ring]
to the severity of impact." Id. at § 1508.27(b).

   The regulation details ten intensity factors to be considered,
of which the plaintiffs direct our attention to five they believe
support the conclusion that an EIS must be prepared. Without
discounting the potential applicability of any of the ten fac-
tors, two in particular militate strongly in favor of the plain-
tiffs’ position. Those are the "[u]nique characteristics of the
geographic area such as . . . wetlands . . . or ecologically criti-
cal areas," id. at § 1508.27(b)(3), and "[t]he degree to which
the effects on the quality of the human environment are likely
to be highly controversial," id. at § 1508.27(b)(4).
           FRIENDS OF BACK BAY v. U.S. ARMY CORPS           15
   The EA acknowledged that Back Bay is part of the
Albemarle-Pamlico Estuarine Sound System, which has been
"designated by EPA as an estuary of national significance."
J.A. 248. The bay has been described "as one of the most
diverse and extensive ecosystems in southeastern Virginia,"
and though its marsh communities are characteristic of the
area and that of northeastern North Carolina, "they are consid-
ered globally rare." J.A. 249. It thus appears beyond question
that the Refuge and its vicinity qualify as unique and ecologi-
cally critical.

   Moreover, the debate concerning the potential effects of the
Wilkins Project on the quality of the human environment in
and around Back Bay has proved to be highly controversial.
We say this not in the sense that all contested actions affect-
ing the environment generate a degree of controversy, particu-
larly among those whose sensitivities may be peculiarly
attuned to such matters, but in the sense that no fewer than
four respected governmental entities (including two of the
Corps’s sister agencies of the federal government) unani-
mously opposed the permit application as proposed. See
Davis v. Mineta, 302 F.3d 1104, 1123 (10th Cir. 2002) (rec-
ognizing that courts "may properly be skeptical" of the factual
basis of agency conclusions "if the responsible agency has
apparently ignored the conflicting views of other agencies
having pertinent expertise" (quoting Sierra Club v. U.S. Army
Corps of Eng’rs, 701 F.2d 1011, 1030 (2d Cir. 1983))).

   The FWS specifically recommended preparation of an EIS
as an alternative to denying the permit, and we agree that is
the preferred approach here. Even were the situation consider-
ably less clear-cut, we remain mindful that "when it is a close
call whether there will be a significant environmental impact
from a proposed action, an EIS should be prepared." Hoffman,
132 F.3d at 18. We concur with the view of the Second Cir-
cuit in Hoffman that the policy goals underlying NEPA are
best served if agencies "err in favor of preparation of an EIS
16         FRIENDS OF BACK BAY v. U.S. ARMY CORPS
when . . . there is a substantial possibility that the [proposed]
action may have a significant impact on the environment." Id.

                               B.

   The plaintiffs also reassert on appeal their contention that,
for several reasons, the permit should not have issued pursu-
ant to § 404 of the CWA. Among other things, the plaintiffs
maintain that, apart from the discrete movement of silt neces-
sary to construct the mooring facility and boat ramp, the
increase in watercraft traffic resulting from completion of the
Wilkins Project may properly be considered as a secondary
effect on the aquatic ecosystem "associated with a discharge
of dredged or fill materials," though the presence of the addi-
tional boats and jet skis "do not result from the actual place-
ment of the dredged or fill material." 40 C.F.R. §
230.11(h)(1); see Fox Bay Partners v. U.S. Army Corps of
Eng’rs, 831 F. Supp. 605 (N.D. Ill. 1993).

   The district court rejected the plaintiffs’ § 404 challenge,
but we need not address it here. Having already concluded
that the Corps’s grant of the permit violated the applicable
NEPA procedural requirements, we are not inclined to decide
whether it should not have issued on different grounds.
Depending on the result of the EIS and the implementation
thereof undertaken by the Corps on remand, the plaintiffs’
CWA objections may not again present themselves. In the
event the issue recurs, however, it can be revisited by the
Corps and, if necessary, the district court, in the normal
course of events.
                              IV.
   Pursuant to the foregoing, we vacate the judgment below
and remand for the district court to remand to the Corps for
preparation of an EIS, and for such other and further proceed-
ings as may be appropriate.
                                VACATED AND REMANDED
