                   United States Court of Appeals
                         FOR THE EIGHTH CIRCUIT
                                     ___________

                                     No. 08-2152
                                     ___________

James G. Thomas; Kerry Thomas;           *
Gregory Norlin; Nancy Norlin;            *
Sierra Club,                             *
                                         *
            Plaintiffs–Appellants,       *
                                         *   Appeal from the United States
      v.                                 *   District Court for the
                                         *   Northern District of Iowa.
Lisa P. Jackson,1 in her capacity        *
as Administrator of the                  *
Environmental Protection Agency;         *
United States Environmental              *
Protection Agency; William W. Rice,2     *
in his capacity as Acting Regional       *
Administrator of Region VII of the       *
Environmental Protection Agency,         *
                                         *
            Defendants–Appellees.        *




      1
        Pursuant to Federal Rule of Appellate Procedure 43(c)(2), Environmental
Protection Agency Administrator Lisa P. Jackson is substituted for former
Environmental Protection Agency Administrator Stephen L. Johnson as Appellee in
this case.
      2
       Pursuant to Federal Rule of Appellate Procedure 43(c)(2), Environmental
Protection Agency Region VII Acting Administrator William W. Rice is substituted
for former Environmental Protection Agency Region VII Administrator John B.
Askew as Appellee in this case.
                                     ___________

                               Submitted: February 11, 2009
                                  Filed: September 10, 2009
                                   ___________

Before LOKEN, Chief Judge, and MELLOY and BENTON, Circuit Judges.
                               ___________

MELLOY, Circuit Judge.

       Plaintiffs filed a complaint in district court3 under the Administrative Procedure
Act (the “APA”), arguing that approval by the Environmental Protection Agency (the
“EPA”) of the State of Iowa’s 2004 “§ 303(d) lists” violated several aspects of the
Clean Water Act (the “CWA”). The district court dismissed the complaint. We
affirm.

                                            I.

A. Statutory and Regulatory Background

      The CWA requires each state to establish water quality standards for bodies of
water within the state’s boundaries. 33 U.S.C. § 1313(a)–(c). To do so, a state first
designates the use or uses of a particular body of water (e.g., water supply, recreation),
see 40 C.F.R. § 131.10, and then designates the water quality criteria necessary to
protect that designated use, id. § 131.11. The water quality standards comprise: (1)
designated uses; (2) water quality criteria defining the amounts of pollutants that the
water can contain without impairment of the designated uses; and


      3
        The Honorable Linda R. Reade, United States District Judge for the Northern
District of Iowa, adopting the Report and Recommendation of the Honorable Jon
Stuart Scoles, United States Magistrate Judge for the Northern District of Iowa.

                                           -2-
(3) anti-degradation requirements, which apply to bodies of water whose quality is
better than required. 33 U.S.C. § 1313(c)(2)(A); 40 C.F.R. §§ 131.6, 131.10–12.

       Section 303(d) of the CWA requires that each state, after establishing its water
quality standards, compile a list of waters, a “§ 303(d) list,” that do not meet those
standards. 33 U.S.C. § 1313(d). In creating its § 303(d) list, a state must “assemble
and evaluate all existing and readily available water quality-related data and
information.” 40 C.F.R. § 130.7(b)(5). The relevant data and information include the
state’s “§ 305(b) report” and its “§ 319 report.” Id. § 130.7(b)(5)(i), (iv). A § 305(b)
report is a water quality assessment report regarding all navigable waters within the
state that each state must submit to the EPA pursuant to CWA § 305(b). 33 U.S.C.
§ 1315(b). The EPA compiles, analyzes, and transmits these § 305(b) reports to
Congress. Id. § 1315(b)(2). A § 319 report is a water quality assessment report
regarding the navigable waters within the state that will fail to meet water quality
standards without limitation of nonpoint sources4 of pollution. Id. § 1329(a).

       Along with the § 303(d) list, the state must submit, inter alia: (1) “[a]
description of the methodology used to develop the list”; (2) “[a] description of the
data and information used to identify waters”; (3) “[a] rationale for any decision not
to use any existing and readily available data and information” for certain categories
of water; and (4) “[a]ny other reasonable information requested by the Regional
Administrator.” 40 C.F.R. § 130.7(b)(6). Since 1992, states have been required to
submit a § 303(d) list to the EPA every two years; states were not required, however,
to submit lists in 2000. See Revision to the Water Quality Planning and Management
Regulation Listing Requirements, 65 Fed. Reg. 17,170 (Mar. 31, 2000). The EPA


      4
        A point source is “any discernible, confined and discrete conveyance,
including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete
fissure, container, rolling stock, concentrated animal feeding operation, or vessel or
other floating craft, from which pollutants are or may be discharged.” 33 U.S.C.
§ 1362(14). A nonpoint source is any other source.

                                          -3-
must approve or disapprove the state’s § 303(d) list within thirty days of its
submission. Id. § 130.7(d)(2). If the EPA disapproves a § 303(d) list, the EPA must
establish its own list for the state within thirty days of the date of disapproval. Id.

       For each water on the § 303(d) list, the state must establish total maximum daily
loads (each a “TMDL”) of certain “pollutants” that the water can sustain without
exceeding water quality standards. 33 U.S.C. § 1313(d)(1)(C); 33 U.S.C. § 1362(6)
(defining “pollutant”). The TMDL includes pollutants from both “point sources” and
“nonpoint sources,” as well as a margin of safety. 40 C.F.R § 130.2(g)–(i). The EPA
must review the state’s TMDLs, and if the EPA disapproves any particular TMDL, the
EPA itself must establish the TMDL. 33 U.S.C. § 1313(d)(2).

       Starting with the states’ 2002 reporting requirements, the EPA recommended
that each state submit an “integrated report” that comprised the state’s § 305(b) report
and § 303(d) list. Robert H. Wayland III, 2002 Integrated Water Quality Monitory
and Assessment Report Guidance (Nov. 19, 2001) (“2002 Report Guidance”). EPA
guidance recommended that the integrated report designate bodies of water as
belonging to one of five categories, which the EPA specified as:

      1. Attaining the water quality standard and no use is threatened.

      2. Attaining some of the designated uses; no use is threatened; and
      insufficient or no data and information is available to determine if the
      remaining uses are attained or threatened.

      3. Insufficient or no data and information to determine if any designated
      use is attained.

      4. Impaired or threatened for one or more designated uses but does not
      require the development of a TMDL.




                                          -4-
             A. TMDL has been completed.

             B. Other pollution control requirements are reasonably expected
             to result in the attainment of the water quality standard in the near
             future.

             C. Impairment is not caused by a pollutant.

      5. The water quality standard is not attained. The [water] is impaired or
      threatened for one or more designated uses by a pollutant(s), and requires
      a TMDL.

2002 Report Guidance. The EPA slightly revised and repeated this recommendation
for 2004 reports. See EPA, Guidance for 2004 Assessment and Reporting
Requirements Pursuant to Sections § 303(d) and 305(b) of the CWA (July 21, 2003)
(“2004 Report Guidance”). Because Category 4C would not be considered a part of
the § 303(d) list, EPA guidance advised that waters that were impaired, but not
impaired by a pollutant, should be omitted from the states’ 303(d) lists. See id. As
discussed below, Plaintiffs contend that the CWA does not allow such a distinction
and that waters that are impaired, but not impaired by a pollutant, must be included
on Iowa’s § 303(d) list.

B. Factual and Procedural Background

       In 1999, the Sierra Club filed a complaint alleging that the EPA had not carried
out its duty to approve or disapprove Iowa’s 1998 § 303(d) list. In 2001, a consent
decree arising from that complaint provided that the EPA had approved part of the
§ 303(d) list, disapproved part, and created a final § 303(d) list. The consent decree
required that TMDLs be established over a ten-year period pursuant to a schedule
agreed by the parties. In evaluating compliance with the TMDL schedule, the EPA
could consider TMDLs established by Iowa and approved by the EPA, TMDLs
established by the EPA, and impaired waters and pollutants the EPA determined do


                                          -5-
not need TMDLs. The consent decree, which is not directly at issue here,
contemplated that water bodies might be removed from future § 303(d) lists as
provided by the CWA and EPA regulations.

       In 2000, Iowa passed its Credible Data Law, Iowa Code § 455B.171, .193–.195,
which limited the data Iowa considers when creating its draft § 303(d) list to data Iowa
considers credible. Id. § 455B.194.1.c. The Credible Data Law provides, inter alia,
that Iowa will presume data over five years old not to be credible. Id. § 455B.171.
The EPA informed Iowa that the restrictions of the new law were inconsistent with the
CWA’s mandate to evaluate all data and that the EPA would be reviewing Iowa’s list
without applying the Credible Data Law. Iowa, nevertheless, followed its Credible
Data Law when preparing its § 303(d) lists.

       On December 17, 2002, Iowa submitted its draft 2002 list to the EPA, along
with a summary of comments it had received on the draft list and a description of the
methodology used to compile the list. Iowa’s draft 2002 list omitted a large number
of waters that had been on the final 1998 § 303(d) list. Iowa’s rationale for omitting
many of the waters was the insufficiency of data, a rationale Iowa considered a flaw
in the original, 1998 analysis. Iowa omitted other waters because new data indicated
the cause of the impairment was flow or habitat alteration, which were not considered
pollutants. After reviewing Iowa’s 2002 § 303(d) list, the EPA approved the list in
part and disapproved the list in part. The EPA approved the omissions of seventy-one
waters, having concluded that Iowa provided sufficient rationale for the exclusions.
The EPA disapproved, however, the omissions of twenty waters. After a public
comment period, the EPA added eighteen of the twenty waters to the final 2002
§ 303(d) list.

      On May 26, 2005, Iowa submitted its draft 2004 list. Waters were removed for
reasons including new data showing lack of impairment and the establishment of a
TMDL. The EPA again approved the list in part and disapproved the list in part. The

                                          -6-
EPA determined that fourteen new waters should be added to the 2004 list and that six
waters included on the 2002 list but not included on the draft 2004 list should not have
been removed. After a public comment period, the EPA added seventeen of the
twenty waters to the 2004 list. As a result, Iowa’s 2004 § 303(d) list does not include
a number of waters that were included on Iowa’s 1998 § 303(d) list. Because the
rationales supporting omission of numerous waters from the 2004 list were originally
forwarded as reasons for delisting in 2002, we refer to the final 2002 and 2004 lists
together as the § 303(d) list.

        On August 10, 2006, Plaintiffs filed a complaint under the APA challenging the
EPA’s approval of Iowa’s § 303(d) list, seeking a declaratory judgment and an order
to set aside the EPA’s approval of the § 303(d) list. The EPA would then be required,
Plaintiffs argue, to prepare a § 303(d) list that complies with the law. After
considering the parties’ briefs on the merits, the district court dismissed the complaint.

                                           II.

       “We review de novo a district court’s decision whether an agency’s action
violates the APA.” Niobrara River Ranch, L.L.C. v. Huber, 373 F.3d 881, 884 (8th
Cir. 2004). “Under the APA, our review of an agency decision is limited.”
Voyageurs Nat’l Park Ass’n v. Norton, 381 F.3d 759, 763 (8th Cir. 2004). After a
searching and careful review of the record, we may set aside the EPA’s action if it is
“‘arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with
law.’” Friends of Richards-Gebaur Airport v. FAA, 251 F.3d 1178, 1185 (8th Cir.
2001) (quoting 5 U.S.C. § 706(2)(A)).

      “Because Congress has not directly spoken to the precise question” before us,
we “look first to the agency regulations, which are entitled to deference if they resolve
the ambiguity in a reasonable manner.” Coeur Alaska, Inc. v. Southeast Alaska
Conservation Council, 129 S. Ct. 2458, 2469 (2009) (internal quotations omitted).

                                           -7-
Where the regulations are also ambiguous, “we next turn to the [agency’s] subsequent
interpretation of those regulations.” Id. Generally, we must “defer to the agency’s
interpretation so long as it is not arbitrary, capricious, an abuse of discretion, or
otherwise not supported by law.” Friends of the Boundary Waters Wilderness v.
Dombeck, 164 F.3d 1115, 1121 (8th Cir. 1999) (internal quotation omitted); see also
Chevron USA, Inc. v. Natural Res. Def. Council, 467 U.S. 837, 842–44 (1984)).

A. Failure to Consider Important Facts and Information

       Plaintiffs contend that the EPA’s partial approval of Iowa’s § 303(d) list was
arbitrary and capricious. Plaintiffs assert that Iowa failed to consider all relevant data,
including its § 305(b) report and its § 319 list, and that the EPA’s approval of Iowa’s
failure to consider the data indicates that the EPA failed to consider important
information when approving the § 303(d) list. The record does not support Plaintiffs’
assertions.

       Plaintiffs most forcefully argue that waters shown in the § 305(b) report as not
meeting their uses, only partially meeting their uses, or with threatened uses should
necessarily be included on the § 303(d) list. Although, generally, Iowa must
“assemble and evaluate” data on each water included in the § 305(b) report when
approving or creating the § 303(d) list, 40 C.F.R. § 130.7(b)(5)(i), the regulations do
not require Iowa to include all § 305(b) waters on its § 303(d) list. Instead, Iowa must
provide documentation to support its determination not to list a particular water. Id.
§ 130.7(b)(6). Here, Iowa provided a rationale for each § 305(b) water that it did not
include on its draft § 303(d) list. The EPA’s ultimate agreement with Iowa’s proposed
conclusion as to a particular water is insufficient, without more, to support a
conclusion that the EPA failed to consider important facts or information in reaching
its conclusion. Plaintiffs have not pointed to any additional evidence, so their
argument fails.



                                           -8-
       Plaintiffs also argue that Iowa improperly omitted numerous bodies of water
that had been included on the 1998 list because Iowa found the original data
insufficient to maintain a listing. Although Iowa is not required to include all § 305(b)
waters on its § 303(d) list, the EPA may—and here, did—require Iowa to show good
cause for not including a water. Id. § 130.7(b)(6)(iv). “Good cause includes, but is
not limited to, more recent or accurate data; more sophisticated water quality
modeling; flaws in the original analysis that led to the water being listed in the
categories in § 130.7(b)(5); or changes in conditions.” Id. Iowa submitted new data
for several delisted waters, but the State delisted many others merely because it now
found the data supporting the 1998 listing insufficient. Plaintiffs argue that “good
cause” requires a showing of “specific data” supporting the rationale. Iowa, however,
asserted that even without “more recent or accurate data” indicating to the contrary,
the insufficiency of the existing data shows “flaws in the original analysis.” The EPA
accepted this rationale as good cause. Plaintiffs, for their part, offer no explanation
or support as to why additional data are required to conclude that the existing data are
insufficient.

       We must first consider the EPA’s interpretation of “flaws in the original
analysis.” Id. § 130.7(b)(iv). As stated above, we owe significant deference to the
EPA’s interpretation of its own regulation. Moreover, we note that the EPA “may”
request a showing of good cause, but the regulations do not require it to do so.
Further, because good cause “includes, but is not limited to . . . flaws in the original
analysis,” id. (emphasis added), the EPA could still determine that insufficiency of the
original data was “good cause” even if not strictly a “flaw[] in the original analysis.”
Id. The optional nature of the good-cause request and the nonrestrictive definition of
good cause reinforces the deference owed to the EPA’s allegedly expansive
interpretation of what constitutes such a flaw in the analysis. Accordingly, we find
no difficulty accepting the EPA’s reasonable interpretation of “flaws in the analysis”
as including the flaw of basing the analysis on insufficient data.



                                          -9-
       We must next consider the EPA’s application of this interpretation to the waters
at issue in the present case. We recognize Plaintiffs’ concern as to declining standards
of analysis and enforcement, but such concerns do not necessarily preclude a
determination that a particular collection or type of data is insufficient to require
inclusion on a § 303(d) list. Notwithstanding the EPA’s earlier determinations
regarding the same data, Plaintiffs have not shown that the EPA’s more recent
determinations are “implausible” or without a “rational connection” to the facts.

       Whether Iowa has shown “good cause” for its determination not to include
§ 305(b) waters on the § 303(d) list is a question for which deference to the EPA’s
judgment requires that we affirm the district court. We defer to both the EPA’s
interpretation of its own regulation and its determination regarding the specific waters
at issue.

B. Waters Not Impaired by “Pollutants”

       Plaintiffs also claim that the EPA erred by allowing Iowa to omit from its
§ 303(d) list waters that were impaired but not impaired by any “pollutant,” as that
term is defined by CWA § 502(6). 33 U.S.C. 1362(6). We will set aside the EPA’s
approval of the § 303(d) list if it is “not in accordance with the law.” 5 U.S.C.
§ 706(A)(2). Plaintiffs contend that the CWA requires all impaired waters, including
those not impaired by a pollutant, to be included on the § 303(d) list.5 The EPA
disagrees, contending that the CWA does not require it to include waters that are
impaired but not impaired by any pollutant.




      5
       Notwithstanding an attack on “[t]he false distinction between pollution and
pollutants,” Plaintiffs do not appear to argue that the causes of the pollution in the
disputed waters are pollutants for purposes of the CWA. Accordingly, we assume,
without deciding, that the waters at issue are not, in fact, impaired by “pollutants.”

                                         -10-
        The CWA does not expressly limit the § 303(d) list to waters impaired by
pollutants. Rather, § 303(d) provides: “Each State shall identify those waters within
its boundaries for which the effluent limitations . . . are not stringent enough to
implement any water quality standard applicable to such waters.” 33 U.S.C.
§ 1313(d)(1)(A). The Ninth Circuit has addressed the interpretation of § 303(d) in
several cases, most recently in Pronsolino v. Nastri, 291 F.3d 1123, 1136–37 (9th Cir.
2002) (holding that § 303(d) lists must include waters impaired only by nonpoint
source pollution). That circuit framed the “precise statutory question” before it as
“whether the phrase ‘are not stringent enough’ triggers the identification requirement
both for waters as to which the effluent limitations apply but do not suffice to attain
water quality standards and for waters as to which effluent limitations do not apply at
all to the pollution sources impairing the water.” Id. at 1126. We consider the same
statutory language here.

        In an earlier case, the Ninth Circuit “read § 303(d)(1)(A) as applying to all
waters in the state, not only to the subset covered by certain kinds of effluent controls.
It understood ‘not stringent enough’ to mean ‘not adequate for’ or ‘inapplicable to.’”
Pronsolino, 291 F.3d at 1137 (discussing Dioxon/Organochlorine Ctr. v. Clarke, 57
F.3d 1517 (9th Cir. 1995)). In Dioxon, the Ninth Circuit held that “the [effluent]
limitations . . . referred to in § 1313(d) are not applicable to toxic pollutants; thus any
limitations required by those provisions of § 1311, as a matter of law, ‘are not
stringent enough’ to achieve established water quality standards. Dioxin, 57 F.3d at
1528. In Pronsolino, the Ninth Circuit relied on its prior holding to conclude that
effluent limitations “are . . . ‘not stringent enough’ to achieve applicable water quality
standards for other waters not subject to those requirements.” Pronsolino, 291 F.3d
at 1137. Similarly, we could conclude that because effluent limitations are not
applicable to non-pollutant impairment, those limitations are “not stringent enough”
to achieve established water quality standards. Although we might find such a reading
to be reasonable, the phrase “not stringent enough” is sufficiently ambiguous to permit



                                           -11-
competing interpretations. See id. at 1135 n.14. (discussing different meanings of
“stringent” and “stringent enough”).

       The Ninth Circuit also noted that a more inclusive § 303(d) list supported the
general purpose of the CWA:

      [T]here is no such distinction with regard to the basic purpose for which
      the § 303(d) list and the TMDLs are compiled, the eventual attainment
      of state-defined water quality standards. Water quality standards reflect
      a state’s designated uses for a water body and do not depend in any way
      upon the source of pollution. . . . § 303(d) is structurally part of a set of
      provisions governing an interrelated goal-setting, information-gathering,
      and planning process that, unlike many other aspects of the CWA,
      applies without regard to the source of pollution.

Id. at1137–38. Still, it is undisputed that the primary, direct purpose of § 303(d) is to
address pollutants, and the arguments supporting the Ninth Circuit’s opinion in
Pronsolino are less persuasive as applied to the present dispute. In Pronsolino, the
Ninth Circuit noted that when determining TMDLs both point sources and nonpoint
sources must be considered. Clearly, the amount of nonpoint source pollutant would
directly affect the amount of point source pollutant a water could satisfactorily sustain.
Here, in contrast, Plaintiffs have made no showing that the impairments at issue would
have more than an indirect effect, if any, on the level of pollutant that would be
allowed under a TMDL. While it may be that addressing broader “impaired by
pollution” concerns would help address the problem of bringing defined pollutants
within set limits, evaluating this indirect relationship requires the EPA’s specialized
knowledge.

      We also note that in both Ninth Circuit cases, the court addressed the issue in
the context of what the EPA was authorized to do, not what it was mandated to do.
While the EPA may be authorized to require the inclusion of the waters now at issue
on Iowa’s § 303(d) list, the EPA is not mandated to include these waters. See id. at

                                          -12-
1141 (holding “that the EPA did not exceed its statutory authority”); cf. Natural Res.
Def. Council v. U.S. E.P.A., 915 F.2d 1314, 1322 n.9 (9th Cir. 1990) (“Those waters
for which limitation based on the more demanding best available technology . . . did
not have to be listed [under § 303(d)].”); Dioxon, 57 F.3d at 1528 n.14 (“Footnote 9
in Natural Resources does, however, suggest that neither the states nor the EPA are
obligated under § 1313(d)(1)(A) to list waters impaired by toxic pollutants despite the
proven failure of [Best Available Technology] limitations.” (emphasis added)).
Although § 303(d) may allow the EPA to include all impaired waters on a state’s
§ 303(d) list, it does not require the EPA to include impaired waters where the EPA
has determined the impairment is due to something other than a pollutant.

C. Iowa’s Methodology

      Plaintiffs also contend that the EPA erred by inappropriately addressing several
aspects of Iowa’s listing methodology.

        Plaintiffs first argue that the implementation of Iowa’s Credible Data Law is,
in effect, a modification of water quality standards and that the EPA cannot approve
the § 303(d) list until it has first approved the modified water quality standards. The
EPA agrees that the Credible Data Law does not comply with the CWA but maintains
that the Iowa law does not constitute a change in water quality standards and that
because the EPA did not rely on the Credible Data Law when approving the § 303(d)
list, the approval was permissible.

       We disagree with Plaintiffs’ contention that when a state uses a non-compliant
variation of approved water quality standards in drafting its § 303(d) list, the ultimate,
EPA-approved list must be invalidated in its entirety even if the EPA applied the
correct water quality standards rather than the non-compliant variation. See Sierra
Club, Inc. v. Leavitt, 488 F.3d 904, 912 n.14 (11th Cir 2007) (rejecting a similar
argument where the court concluded that the record showed the EPA applied the

                                          -13-
approved standards rather than the challenged variation); see also 40 C.F.R.
§ 130.7(d)(2) (establishing a time frame for the EPA to develop § 303(d) list if it
disapproves the state’s draft list). However, if the EPA were to itself apply the
unapproved state modification, the resulting § 303(d) list would be undermined.
Florida Public Interest Research Group Citizen Lobby v. EPA, 386 F.3d 1070,
1090–91 (11th Cir. 2004) (“FPIRGCL”) (remanding for additional review where the
court concluded that the record showed that the EPA applied the challenged variation
rather than the standards as approved).

        Here, the record shows that the EPA repeatedly informed Iowa that the use of
the Credible Data Law violated the CWA; that the EPA informed Iowa that the EPA
would review Iowa’s § 303(d) list “in accordance with existing federal regulations”
rather than in accordance with the Credible Data Law; that the EPA requested that
Iowa supply the EPA with all data excluded from consideration under the Credible
Data Law; and that Iowa did provide additional data in response to the EPA’s request.
The EPA then added several waters to the § 303(d) list based on its review of this
additional information. The only evidence in the record that the EPA impermissibly
relied on the Credible Data Law is an inference resulting from the fact that the EPA
decided not to add the majority of the waters back to Iowa’s § 303(d) list. This case
is thus distinguishable from FPIRGCL, where the EPA adopted the state methodology
to the extent the EPA deemed the methodology reasonable. See 386 F.3d at 1078–79
& n.10 (“[T]he EPA found the [state’s] exclusion of data older than 7.5 years to be
‘reasonable,’ and accordingly adopted the same time frame in its own review.”). On
the record before us, the fact that the EPA ultimately agreed with Iowa’s conclusions
concerning the majority of waters is insufficient to meet Plaintiffs’ burden to show
that the EPA, after requiring the state to submit the excluded data, then adopted
Iowa’s methodology of excluding that data from evaluation.

       Second, Plaintiffs contend that the EPA impermissibly accepted Iowa’s
distinction between “evaluated” and “monitored” waters and its position that waters

                                        -14-
evaluated, but not monitored, need not be placed on the § 303(d) list.6 The EPA
maintains that it reviewed all “evaluated” waters consistent with federal regulations,
ignoring Iowa’s distinction. As with the Credible Data Law, Plaintiffs’ only evidence
that the EPA adopted Iowa’s distinction is the fact that the EPA only added four of the
“evaluated” waters back to the § 303(d) list. Plaintiffs argue that “[w]e must assume”
that the EPA approved of Iowa’s distinction. The burden of proof lies with Plaintiffs,
however, and Plaintiffs cannot meet that burden through unsupported assumptions.

       Finally, Plaintiffs contend that even relying on the approved water quality
standards was in error because Iowa was in the process of revising its water quality
standards. The EPA counters that applicable water quality standards remain in effect
until the new standards are approved. See 40 C.F.R. § 131.21(e) (“A State or
authorized Tribe’s applicable water quality standard for purposes of the Act remains
the applicable standard until EPA approves a change, deletion, or addition to that
water quality standard, or until EPA promulgates a more stringent water quality
standard.”). As Plaintiffs have pointed to no authority to the contrary, and any
improper delay in the promulgation of the revised standards is not directly at issue in
the case before us, we defer to the EPA’s reasonable application of its own
regulations. We also note that Plaintiffs’ suggestion could be counterproductive, as
waiting for revisions to the standards would result in continued delays in producing
any § 303(d) list. Concerns that a particular list will be based on imperfect, though
approved, standards are mitigated by the periodic nature of the list.




      6
       Iowa’s methodology considered only “monitored” waters as eligible for
inclusion on the state’s § 303(d) list. Iowa describes “monitored waters” as those “for
which the use support decision is principally based on current site-specific data.”
Iowa considers waters to be only “evaluated,” and thus not considered for inclusion
on the state’s § 303(d) list, if the relevant data is “other than current site-specific
data.”

                                         -15-
                                  III.

For the foregoing reasons, we affirm the judgment of district court.

                ______________________________




                                 -16-
