Opinion by Judge BRUNETTI; Dissent by Judge REINHARDT.

BACKGROUND

Petitioners representing environmental and fishing interests 1 challenge final actions of the Bonneville Power Administration (BPA) 2 in these consolidated petitioners for review. In 1990, BPA entered into agreements with British Columbia Hydro and Power Authority (BC Hydro) and several electric utilities, known as the Mid-Columbia Participants, 3 governing rights to water stored behind hydroelectric dams on the Columbia River system in Canada. Petitioners argue that BPA ignored its statutory duty to provide equitable treatment for fish and wildlife on the river by entering into these agreements. Petitioners also argue that BPA violated the National Environmental Policy Act by failing to prepare an Environmental Impact Statement.

There is no single “Law of the River” on the Columbia. Rather, as we consider BPA’s decision to enter into these two agreements we must navigate a maze of overlapping treaties, laws, and regulations, which together *1525 attempt to balance the varied interests on the river. Prominent among the laws on the river are the United States-Canada Columbia River Treaty, the Northwest Power Act, and the National Environmental Policy Act (NEPA). Subsequent to the submission of this case for decision, the Endangered Species Act (ESA) began playing a significant role. See, e.g., Ramsey v. Kantor, 96 F.3d 434 (9th Cir.1996); Aluminum Co. of America v. National Marine Fisheries Serv., 92 F.3d 902 (9th Cir.1996); Idaho Conservation League v. Thomas, 91 F.3d 1345 (9th Cir.1996); Idaho Dep’t Fish & Game v. National Marine Fisheries Serv., 56 F.3d 1071 (9th Cir.1995). It is important to understand both the terms of the agreements, and the law of the river ,as it existed when BPA entered into them, to properly analyze BPA’s decision to enter into the NTSAs.

Columbia River Treaty

The 1964 Columbia River Treaty between the United States and Canada provided for building four storage reservoirs: three in Canada (Mica, Kennleyside, and Duncan) and one in the United States (Libby). The reservoirs that were built and operated under the Treaty represent almost half the water storage on the Columbia River System. The Treaty required 15.5 million acre-feet of Canadian storage, but reservoirs actually built contained storage' capacity of 20.5 million acre-feet. The excess storage capacity, most of which is behind Mica Dam, is referred to as non-Treaty storage. The Non-Treaty Storage Agreements, discussed below, were necessary to govern the rights to this additional storage capacity. Nothing in the Treaty prevented Canada from using all of the non-Treaty storage unilaterally, although the United States argued it had the right to compensation if use of the non-Treaty storage resulted in reduced Columbia River flows in the United States.

Northwest Power Act

In 1980, Congress enacted the Northwest Power Act (NPA), 16 U.S.C. §§ 839 -839h, which “marked an important shift in federal policy.” Northwest Resource Information Center v. Northwest Power Planning, 35 F.3d 1371, 1377 (9th Cir.1994). “Continually declining fish runs had revealed the failures of previous legislative efforts requiring that ‘equal consideration’ be given to fish and wildlife affected by resource exploitation.” Id. The NPA created “a pluralistic intergovernmental and public review process.” Id. at 1378 . At the hub of this process, Congress established the Pacific Northwest Electric Power and Conservation Planning Council (Council), directing it to create “a program to protect, mitigate, and enhance” the Columbia River Basin’s fish and wildlife “to the extent affected by the development and operation of the Basin’s hydropower system.” 4 16 U.S.C. § 839b(h)(l)(A), (h)(10)(A). The Council’s authority with respect to fish and wildlife measures is constrained; the Council “can guide, but not command, federal river management.” 16 U.S.C. §§ 839b(h)(10), 839b(i), 839b(j); see also Northwest Resource Information Center v. National Marine Fisheries Serv., 25 F.3d 872 , 874 (9th Cir.1994).

Under this statutory scheme, the BPA Administrator has two responsibilities: First, the Northwest Power Act requires the Administrator to exercise his responsibilities under the Act “in a manner that provides equitable treatment” for fish and wildlife. 16 U.S.C. § 839b(h)(ll)(A)(i). Second, the Administrator must take into account “to the fullest extent practicable, the program adopted by the Council.” 16 U.S.C. § 839b(h)(ll)(A)(ii). Attempting to balance environmental and energy considerations, the Act states that fish and wildlife protection measures cannot jeopardize “an adequate, efficient, economical, and reliable power supply.” 16 U.S.C. § 839b(h)(5).

Since the adoption of the Northwest Power Act, BPA has exercised .its responsibility to take into account the Council’s Program by adopting many of the Program’s essential fish protection measures. First, BPA *1526 adopted the centerpiece of the Council’s 1987 Program, the “Water Budget,” which is a volume of water to be released during the spring in order to “create an artificial freshet that speeds juvenile fish to the ocean.” O.R. at 2856. To assist migrating juvenile salmon, the Council established a water budget of 1.19 million acre-feet for the Snake river and 3.45 million acre-feet for the Columbia. Second, BPA agreed to spill water through a spillway, rather than the dam’s turbines, which assists juvenile passage through dams. Third, BPA funded fish hatcheries throughout the Columbia River Basin.

After the implementation of the Council’s 1987 Fish and Wildlife Program, BPA adopted further protective measures for ana-dromous fish. In 1988, BPA entered in the Vernita Bar Agreement with the Mid-Columbia utility districts to protect chinook spawning, incubation and emergence on Vernita Bar. In 1989, BPA entered into a spill agreement with several fish agencies and the U.S. Army Corps of Engineers.

The Council’s Program, and BPA’s implementation of the Program, failed to reverse the trend of decreasing fish populations on the Columbia. See generally Northwest Resource Information Center, Inc. v. Northwest Power Planning Council, 35 F.3d 1371, 1381-84 (9th Cir.1994). Salmon and steel-head populations continued to decline through 1990. Id. at 1381 . In 1990, environmental advocates petitioned the National Marine Fisheries Service to list three Snake River stocks and one Columbia River stock under the Endangered Species Act. Id. In response to the endangered species petitions, various political leaders convened a “Salmon Summit” to develop a comprehensive plan to enhance fish populations on the Columbia. The result of the “Salmon Summit” was the development of the “Strategy for Salmon” which has also been attacked as inadequate. Id. Congress’ declared goal “to protect, mitigate and enhance the fish and wildlife” populations on the Columbia River, 16 U.S.C. § 839 (6), was still unmet ten years after the passage of the Northwest Power Act.

Non-Treaty Storage Agreements

In the early 1980s, a dispute arose between Canada and the United States regarding the use of non-Treaty storage. BC Hydro asserted its right to use the non-Treaty storage unilaterally, while BPA contended that it was entitled to compensation for any reduction in flows that would result if BC Hydro filled the non-Treaty storage. The parties negotiated a compromise by entering into a Non-Treaty Storage Agreement in 1983. This original fourteen-month agreement was superseded in 1984 with a ten-year agreement in which BPA and BC Hydro agreed to share equally in 2 million acre-feet of water in non-Treaty storage space.

In 1987, BPA and BC" Hydro agreed to study methods of increasing the efficient operation of the Columbia River hydrosystem without constructing new facilities. The result of these negotiations was the 1990 Non-Treaty Storage Agreement (NTSA or BC Hydro NTSA), which is the subject of this litigation. The NTSA expanded the amount of non-Treaty storage capacity from 2 million acre-feet to about 4.5 million acre-feet, and extended the agreement from 1993 — when the old agreement expired — to the year 2003.

The BPA Administrator signed the agreement after a two-year public process involving written comments and public meetings. During the process, BPA circulated a draft Environmental Assessment (EA). It issued a final EA after receiving comments-on the draft. The U.S. Department of Energy issued a Finding of No Significant Impact (FONSI) on June 25, 1990, and the Administrator issued his NTSA Decision Record and signed the NTSA on July 9, 1990. BPA explains that it entered the NTSA with BC Hydro in part because the Council encouraged it to take actions to offset the loss of power and annual revenue caused by compliance with the Water Budget. It asserts that “the NTSA does not compel any particular allocation” of non-Treaty storage. Official Record (“O.R.”) at 1337.

During the public comment process leading up to the NTSA, BPA held a series of *1527 public meetings with federal and state fish and wildlife agencies, Indian Tribes, utilities, and the public to exchange information and discuss the proposed NTSA. O.R. at 1324-25. Various fishery advocates comprising the Columbia Basin Fish and Wildlife Authority (CBFWA) focused their comments regarding the NTSA on two issues: (1) a concern that the NTSA would negatively impact fisheries interests; and (2) a request that the non-Treaty storage be dedicated to increase flows for anadromous fish. Id.

In response to CBFWA’s first concern, BPA entered into a separate non-Treaty storage agreement (NTS Fish and Wildlife Agreement). O.R. at 1485-90. This agreement ensures that non-Treaty storage will not be operated in a manner which harms fish and wildlife. O.R. at 1338, 1485-1505. Second, the agreement guarantees that non-Treaty storage will not disrupt existing fish protection measures, such as the Vernita Bar Agreement and the Water Budget. O.R. at 1490. Third, BPA agreed to fund a study regarding the rental of irrigation water in Idaho to augment Snake River flows, and to provide further funds for renting the water, if feasible. O.R. at 1491-92.

Finally, BPA entered into a third agreement, which petitioners challenge along with the BC Hydro NTSA. Approximately six months after entering into the NTSA, BPA entered into a power agreement with several utility districts known as the Mid-Columbia Participants. Through this agreement (MCP NTSA), BPA contracted to use some of its share of the non-Treaty storage capacity. The MCP NTSA was made subject to the NTS Fish and Wildlife Agreement. The Mid-Columbia Participants could not, therefore, use their share of the non-Treaty storage water in a manner that would cause adverse effects on the fish to be “greater than would have occurred in the absence of non-Treaty storage.” O.R. at 1337, 1489.

DISCUSSION

Petitioners argue that BPA violated the Pacific Northwest Electric Power Planning and Conservation Act (Northwest Power Act or NPA), and the National Environmental Policy Act (NEPA) by entering into the BC Hydro NTSA and the MCP NTSA. 5 For relief, petitioners ask this court (1) to invalidate both the BC Hydro NTSA and the MCP NTSA, and (2) to enjoin BPA from implementing the NTSA agreements until an EIS is prepared. We exercise original jurisdiction over this action pursuant to 16 U.S.C. § 839f(e). Northwest Resource Information Center v. National Marine Fisheries Serv., 25 F.3d 872 (9th Cir.1994).

I.

SUPPLEMENTAL AFFIDAVITS

Before addressing petitioners’ claims that BPA violated the NPA and NEPA, we must first address whether we may consider affidavits submitted by petitioners on appeal. Petitioners have submitted four affidavits in an attempt to establish standing before this court. BPA and the Mid-Columbia Participants moved to strike the affidavits on the grounds that petitioners inappropriately attempted to supplement the administrative record and expand the scope of this litigation. Alternatively, they asked that we allow them to file a supplemental response. Petitioners replied that they submitted the affidavits for the sole purpose of establishing standing. We deny respondents’ motion to strike and the alternative motion for leave to file a supplemental response.

BPA cited several cases for the proposition that parties appealing agency decisions cannot supplement the record on appeal. These cases are inapposite because they address the merits of the agency decision rather than standing to challenge that decision in a federal court. See, e.g., Seattle Community Council Fed’n v. FAA, 961 F.2d 829 , 834 n. 3 (9th Cir.1992). Because Article Ill’s standing re *1528 quirement does not apply to agency proceedings, petitioners had no reason to include facts sufficient to establish standing as a part of the administrative record. We therefore consider the affidavits not in order to supplement the administrative record on the merits, but rather to determine whether petitioners can satisfy a prerequisite to this court’s jurisdiction. Didrickson v. United States Dep’t of Interior, 982 F.2d 1332 , 1340 (9th Cir.1992) (accepting appellant-intervenors’ supplemental declarations alleging particularized injury because intervenors were not required to establish standing until they appealed).

BPA also argues that the Supreme Court’s decision in Lujan v. Defenders of Wildlife, 504 U.S. 555 , 112 S.Ct. 2130 , 119 L.Ed.2d 351 (1992), requires that petitioners establish standing in their opening brief. In Defenders of Wildlife , the Supreme Court discussed the quantum of proof required of plaintiffs at the pleading, summary judgment, and trial phases of litigation in district court. Id. at 561 , 112 S.Ct. at 2136-37 . This case is quite different than the examples cited by the Supreme Court, because here we have original jurisdiction. As we have previously noted, “[t]he original jurisdiction granted this court by ... 16 U.S.C. § 839f(e)(5), raises procedural problems that will have to be resolved on a ease-by-case basis.” California Energy Resources Conservation & Dev. Com’n v. Johnson, 807 F.2d 1456 , 1465 n. 7 (9th Cir.1986). Determining standing is essentially a legal inquiry but may involve underlying factual findings. American-Arab Anti-Discrimination Comm. v. Thornburgh, 970 F.2d 501 , 506 (9th Cir.1991). Because standing was not at issue in earlier proceedings, we hold that petitioners in this case were entitled to establish standing anytime during the briefing phase. We consider the affidavits solely to determine whether petitioners have standing to bring this action.

We deny BPA’s alternative motion for leave to file a supplemental response because, from the content of the motion and the representations of counsel at oral arguments, it became clear that BPA wishes to respond only to the affiants’ criticisms of BPA’s implementation of the NTSA’s and the Fish and Wildlife Agreement. As BPA points out, however, implementation of the agreements is not before this court. The profferred response is therefore irrelevant.

II.

NORTHWEST POWER ACT

Petitioners argue that BPA violated the Northwest Power Act by failing to provide equitable treatment for fish and wildlife. They argue that BPA acted inequitably towards the fish in that (1) the NTSAs will cause a reduction in the number of fish on the river; and (2) by entering into the NTSAs, BPA benefitted power interests without guaranteed and concomitant benefits for fish. In addition to their equitable treatment claim, petitioners argue that BPA failed to comply with the Act’s procedures for the acquisition of major resources.

A.

Standing

As a threshold issue, BPA argues that petitioners lack standing to raise their Northwest Power Act claim. To establish standing petitioners “must have suffered an injury in fact — an invasion of a legally protected interest which is (a) concrete and particularized, and (b) actual or imminent, not conjectural or hypothetical.” Lujan v. Defenders of Wildlife, 504 U.S. 555, 560 , 112 S.Ct. 2130, 2136 , 119 L.Ed.2d 351 (1992) (internal citations and quotations omitted). In addition, petitioners must show that such injury is fairly traceable to the challenged action. Id. Finally, they must show that it is likely that the injury will be redressed by a foreseeable decision. Id. The party invoking federal jurisdiction bears the burden of establishing standing. Id. Standing must be supported in the same way as any other matter on which the plaintiff bears the burden of proof.

The supplemental affidavits submitted by the petitioners are sufficient to establish that any injury to fish and wildlife interests on the Columbia River would *1529 cause injury to each petitioner. 6 The more difficult issue for petitioners is demonstrating that the NTSAs will cause injury to the fish. First, petitioners argue that the NTSAs will cause harm to fish by reducing their stocks on the river. They claim that BPA’s environmental assessment itself, prepared prior to entering into the NTSAs, identifies negative impacts to salmon as a likely result of BPA’s decision to enter into the NTSA and MCP NTSA. The portion of the EA to which petitioners refer, states:

O.R. at 1278. Contrary to petitioners’ claim, this statement does not show that the harm to the fish is a likely result of the NTSA. Petitioners submit no evidence rebutting BPA’s conclusion that the NTSAs’ effects on fish populations were insignificant. Petitioners’ claim of injury, therefore, is too speculative, falling far short of the Court’s requirement that the injury be “certainly impending.” See Defenders of Wildlife, 504 U.S. at 564 n. 2, 112 S.Ct. at 2138 n. 2. Here, it is just as likely that BPA’s decision to enter into the NTSAs will result in an increase in the fish population as a decrease.

Petitioners also argue that BPA’s responsibility to provide equitable treatment for fish and wildlife required BPA to dedicate a portion of the non-Treaty storage capacity for the benefit of fish. 7 If the Northwest *1530 Power Act guarantees the fish a portion of the non-Treaty storage, it is clear that a denial of this great benefit would injure the fish; consequently, petitioners would be injured and they would have standing to sue. Therefore, we will address the merits of petitioners Northwest Power Act claim to determine whether the Act requires BPA to dedicate a portion of the non-Treaty storage for the benefit of the fish.

B.

Standard of Review

“[W]e review the construction of a statute de novo as a question of law, [but] we accord substantial deference to the interpretation given statutes by the officers or agency charged with their administration.” Central Montana Elec. Power Coop. v. Administrator of Bonneville Power Admin., 840 F.2d 1472 , 1476 (9th Cir.1988) (citations omitted). To uphold BPA’s interpretation of the Northwest Power Act, we “need only conclude that it is a reasonable interpretation of the relevant provisions.” Id. at 1476-77 (quotations and citations omitted).

C.

Equitable Treatment

Petitioners argue- that once BPA gained control over 2.25 million acre-feet of the non-Treaty storage capacity, it was required, under the Northwest Power Act, to dedicate a portion of that water to benefit fish and wildlife interests. According to this argument, the fish are not worse off as a result of the NTSAs. Rather, petitioners argue, if BPA enters into a contract benefit-ting power, it must contract an equal benefit for fish. Petitioners claim to a dedicated portion of the non-Treaty storage is of great importance. The precipitous decline in salmon population has reached a crisis level. Because the resources of the river have been overtapped, many commentators have noted the need for additional sources of water. The prospect of seizing upon Canadian storage has been seen by some commentators as the solution to the river’s problems.

Daniel Rohlf, “Colloquim: Who Runs the River?” 25 Envtl L. 413, 415 (1995).

Petitioners have seized upon the Northwest Power Act as the means to obtain a share of the Canadian storage for fish and wildlife. The basis for petitioners’ claim to a portion of the non-Treaty storage capacity is BPA’s obligation to provide equitable treatment for fish and wildlife interests. The Northwest Power Act directs the Council to “promptly develop and adopt ... a program to protect, mitigate, and enhance fish and wildlife, including related spawning grounds and habitat, on the Columbia River and its tributaries.” 16 U.S.C. § 839b(h)(l)(A). The centerpiece of the program adopted by the Council is the Water Budget, a volume of water released in the spring to assist juvenile anadromous fish in their migration. The Northwest Power Act requires BPA to “exercise [its] responsibilities taking into account at each relevant stage of decisionmaking processes to the fullest extent practicable, the program adopted by the Council.” 16 U.S.C. § 839b(h)(ll)(A)(ii). In addition, the Act imposes upon BPA an independent duty to

16 U.S.C. § 839b(h)(ll)(A)(ii). These two paragraphs in Section 839b(h)(ll)(A) define distinct duties. First, under paragraph (ii), BPA must take the Council’s Fish and Wildlife Program into account to the fullest extent possible. See Northwest Resource Information Center, Inc. v. Northwest Power Planning Council, 35 F.3d 1371 (9th Cir.1994) (NRIC). Second, under paragraph (i), BPA has an independent, substantive obligation to insure equitable treatment. See Public Utility Dist. No. 1 of Douglas County v. Bonneville Power Admin., 947 F.2d 386, 392-94 (9th Cir.1991); Confederated Tribes and Bands of the Yakima Indian Nation v. Federal Energy Regulatory Com’n, 746 F.2d 466, 473 (9th Cir.1984).

This statutory regime requires two levels of consideration for fish and wildlife. The primary fish and wildlife protection measures are intended to be established through the Council’s Program. The statutory structure of the Northwest Power Act makes it clear that the Program was to be developed through a detailed and deliberate process of consultation with fishery managers who have great experience and expertise with fish and wildlife protection. See NRIC, 35 F.3d at 1388. Section (a)(1) of the Act establishes the Council and directs it to adopt a “program to protect, mitigate, and enhance fish and wildlife, and to otherwise expeditiously and effectively carry out the Council’s responsibilities and functions under this chapter.” 16 U.S.C. § 839b(a)(l)(B). In developing its Program, the Council is required to request recommendations from the “Federal, and the region’s State, fish and wildlife agencies and from the region’s appropriate Indian tribes.” 16 U.S.C. § 839b(h)(2). The Council is not permitted to simply disregard this advice from fishery managers. Rather, “[t]he Council shall develop a program on the basis of such recommendations.” 16 U.S.C. § 839b(h)(5). Finally,

16 U.S.C. § 839b(h)(7).

In NRIC, “the Council rejected the consensus of agencies and tribes that flows should be significantly increased, and adopted flows very close to those recommended by power interests.” NRIC, 35 F.3d at 1382. NRIC and the Yakima Nation argued that the Council failed to explain, in the Program, a statutory basis for its rejection of river flow recommendations of fishery managers. Id. at 1384. We held that the mandatory language.in the Northwest Power Act required the Council to state, in its final decision, why it rejected the recommendations of the fishery managers. Id. at 1385.

Further, we rejected the Council’s argument that the Act’s requirement that it give “due deference” to the fishery managers requires only nominal deference. . We explained that “Congress realized that furtherance of the purpose of the Act, that fish and wildlife be on a par with energy, required that the Council defer to the recommendations of agencies and tribes.” Id. at 1388. We noted that the reason for the high degree of deference to the fishery managers was their “unique experience and expertise in fish and wildlife.” Id.

The Northwest Power Act thus requires the Council to adopt a fish and wildlife program that includes the recommendations of *1532 the fishery managers with their great expertise in fish and wildlife regulation. Although the Council’s Program is not binding on BPA, BPA is required to take into account the Council’s Program to the fullest extent possible. In this case, petitioners do not argue that BPA has failed to take the Council’s Program into account. Indeed, BPA has adopted the central provisions of the Council’s fish and wildlife program, including the Water Budget.

However, as we have stated before, BPA’s responsibilities to protect fish and wildlife do not end with even complete adoption of the Council’s Program. In Confederated Tribes, 746 F.2d at 473 , we held that BPA’s equitable treatment obligation is “substantive,” and in Public Utility Dist. No. 1 of Douglas County, 947 F.2d at 392 , we held that the obligation is “independent” of BPA’s responsibility to take into account the Council’s Program. However, we have not yet determined the extent of BPA’s responsibilities to provide equitable treatment. We now turn to the question whether this provision of the Northwest Power Act requires BPA to dedicate a portion of the non-Treaty storage capacity to benefit fish.

In Confederated Tribes, we granted a petition for review and directed the Federal Energy Regulatory Commission (FERC) to consider fishery issues prior to granting a forty-year renewal of a power license to the Che-lan public utility district. FERC had begun hearings to develop fish and wildlife protection measures on the Mid-Columbia, but before these proceedings were concluded, FERC granted the license renewal. FERC argued that it was not required to consider fish and wildlife prior to granting the renewal because the license contained a provision that would allow it to impose fish and wildlife protection measures once the Mid-Columbia proceedings were complete. We rejected FERC’s contentions, largely on the basis that FERC violated the Federal Power Act.

However, because the 'issue had been raised by the petitioners, we also considered FERC’s obligation under the Northwest Power Act. Id. at 473 . We noted that “[o]ne purpose of the [Northwest Power Act] is to place fish and wildlife concerns on equal footing with power production.” Id. We then held that FERC failed to meet its obligation to give fish “equitable treatment” under the Northwest Power Act. Id. Although Confederated Tribes provides a useful first examination of BPA’s paragraph (i) responsibilities, it does not help resolve the more difficult questions presented in this case. In Confederated Tribes, FERC completely failed to consider the license renewal’s potential impact on fish and wildlife. In this case, BPA had the benefit of the Council’s Program, which it then implemented.

In Public Utility Dist. No. 1 of Douglas County , we explained one additional element of BPA’s responsibilities under paragraph (i). We explained for the first time that a federal agency could not satisfy its equitable treatment responsibilities under paragraph (i) simply by adopting the Council’s program under paragraph (ii). 947 F.2d at 392 . We recognized that if the Council’s Program fails to ensure adequate fish survival, BPA would be required to take additional measures under paragraph (ii). Id.

Public Utility Dist. No. 1 of Douglas County , like Confederated Tribes, falls short of providing clear guidance in this case. The court in Public Utility Dist. No. 1 of Douglas County was not presented with a situation, as we are here, where the Council’s Program is alleged to be inadequate. The court was simply interpreting the second sentence of 16 U.S.C. § 839b(h)(ll)(A)(ii), which requires BPA to compensate private losses resulting from its imposition of fish protection “measures.” 947 F.2d at 391 . The court rejected BPA’s construction that the Act should be read to distinguish between Program measures and non-Program measures. Id. at 392 . The court held that BPA may undertake protection measures under the Program, or in addition to the Program if the Program is insufficient. Id. In either case, we held, BPA was required to compensate for losses.

Echoing the court’s admonition in Public Utility Dist. No. 1 of Douglas County , petitioners argue that the Council's Program was insufficient at the time BPA entered into the NTSAs. Indeed, petitioners argue that the Council itself recpgnized the inadequacy of *1533 its Program. The Council recognized improvements in main stem flows for fish as “crucial,” O.R. at 2843, and recommended that hydrosystem managers examine the “[f]easibility of using uncontracted water stored in existing reservoirs.” O.R. at 2896. Accordingly, petitioners argue that BPA was required to take additional measures to insure the survival of fish and wildlife. Specifically, petitioners suggest that since BPA gained control over a considerable amount of water through the BC Hydro NTSA, BPA should have dedicated a portion of that water to benefit fish.

We reject petitioners’ suggestions that BPA was required, at the time it entered into the NTSAs, to dedicate a portion of the water for fish. We are aware of no requirement that an allocation among uses be made at the time of BPA’s entering into the agreements. Although the MCP NTSA provides that some of its non-Treaty storage capacity will be used for power purposes, the vast majority of BPA’s share of the non-Treaty storage capacity is unallocated, and BPA may well decide that its responsibilities to provide equitable treatment require it to use a reasonable portion of this water for the benefit of fish. We are left to speculate about how much water BPA will dedicate for fish and wildlife. It may be that BPA would violate its paragraph (i) obligations by using a disproportionate amount of its non-Treaty storage capacity for power purposes. At this point, however, it is premature for petitioners to argue that BPA has violated its paragraph (i) obligations. While BPA could have attempted to negotiate agreements that would have required BC Hydro and the Mid-Columbia Participants to use a portion of their share of non-Treaty storage to benefit salmon, BPA may also benefit salmon by dedicating its own share for that purpose. The court’s role is not to dictate in advance how BPA is to exercise its obligations under the Northwest Power Act. Our role is to review BPA’s actions, once made, to determine whether it has provided equitable treatment. The mere fact that it has allocated a comparatively small portion of the supplemental reserve is not enough to invoke that authority.

Furthermore, in the Administrator’s Decision Record on the NTSA, BPA took the position that the equitable treatment provision describes a balancing test:

O.R. at 1331. BPA’s view that it must balance power needs and wildlife needs on a system-wide basis is a reasonable reading of the . Northwest Power Act. Section 839b(h)(ll)(A) does not explicitly require that each action individually provide equitable treatment. Moreover, in its directive to the Counqil, Congress recognized the need for a comprehensive approach to fish and wildlife protection on the Columbia:

16 U.S.C. § 839b(h)(l)(A). Congress thus recognized that each human use of the Columbia Basin is interrelated to the health of the entire ecosystem. Cf. Alaska Ctr. for the Environment v. Browner, 20 F.3d 981 , 985 (9th Cir.1994) (finding that Congress considered all waters within a state interrelated for Clean Water Act purposes). While each power marketing action that affects the system implicates the equitable treatment provision, BPA may properly exercise its obli *1534 gation by insuring equitable treatment for fish on a system-wide basis.

We emphasize that “equitable treatment” is a highly fact-specific determination. We find it important in this case that: (1) BPA’s environmental assessment shows, and petitioners do not present evidence to the contrary, that the NTSAs will not significantly impact the fish population of the river; (2) BPA signed the NTS Fish and Wildlife Agreement, making guarantees that BC Hydro’s and the Mid-Columbia Participants’ use of non-Treaty storage would not have a deleterious effect on fish and wildlife; and (3) BPA has left unallocated most of its 2.25 million acre-feet share of the 4.5 million acre-feet of non-Treaty storage. Under these circumstances, and in light of BPA’s system-wide approach to its equitable treatment responsibilities, we think it is premature to determine whether BPA has satisfied its obligations. We make this determination only on the record before us, and only to determine that BPA did not violate the Northwest Power Act by entering into the NTSAs.

Although we hold that BPA need not undertake an equitable treatment analysis for every discrete power marketing decision, BPA should nonetheless develop a mechanism for fulfilling its obligation under paragraph (i). Without any guidance from BPA, it is difficult for a reviewing court to determine whether BPA has properly exercised its equitable treatment responsibilities. In this case, we find it is premature to consider petitioners’ claims. Once BPA allocates the non-Treaty storage, however, BPA will be required to demonstrate, by means that allow for meaningful review, that it has treated fish and wildlife equitably.

D.

Resource Acquisition

Petitioners also argue that the NTSA violates the Northwest Power Act because BPA failed to comply with the Act’s procedures for the acquisition of major resources detailed in section 6(e), 16 U.S.C. § 839d(c), which include the requirement that BPA submit the NTSA to the Council for a review of its consistency with the Council’s Power Plan. BPA contends that (1) petitioners are precluded from asserting this claim because they did not raise it during the public process; and (2) the NTSA was not a resource acquisition.

1.

Vermont Yankee Doctrine

BPA cites Vermont Yankee Nuclear Power Corp. v. NRDC, 435 U.S. 519, 553 , 98 S.Ct. 1197, 1216-17 , 55 L.Ed.2d 460 (1978), and Havasupai Tribe v. Robertson, 943 F.2d 32, 34 (9th Cir.1991), for the proposition that petitioners cannot challenge the NTSA on the basis that section 6(c) because they never raised the issue during the public process. 8 In Vermont Yankee, the Court stated that those who wish to have input into the NEPA process have an obligation to structure their participation so that it alerts the agency to their contentions. 435 U.S. at 553 , 98 S.Ct. at 1216-17 . In Havasupai Tribe , the court expressed concern that the Tribe did not raise its claim of inadequate consideration of groundwater impacts until after the final EIS was issued. Nevertheless, it reached the Tribe’s claim. 943 F.2d at 34 .

We have held that the language in Vermont Yankee does not “establish a broad rule which would require participation in agency proceedings as a condition precedent to seeking judicial review of an agency decision.” Kunaknana v. Clark, 742 F.2d 1145, 1148 (9th Cir.1984). The Kunaknana court stated:

Id. (citations omitted).

Vermont Yankee and Havasupai Tribe involved the failure to raise a specific factual contention regarding the substantive content of an EIS during the NEPA public comment process. See also Citizens for Clean Air v. EPA 959 F.2d 839 , 846-47 (9th Cir.1992). In contrast, petitioners in the present ease contest an alleged procedural violation of a statute that governs the public comment process. While it would have been preferable to raise the issue earlier, BPA has a duty to comply with public participation processes provided for in the Northwest Power Act regardless of whether participants complain of violations. We therefore reach the merits of petitioners’ section 6(c) claims.

2.

The NTSA Is Not a Major Resource Acquisition

The Northwest Power Act defines major resource as “any resource that (A) has a planned capability greater than fifty average megawatts, and (B) if acquired by the Administrator, is acquired for a period of more than five years.” 16 U.S.C. § 839a(12). In its policy addressing “the types of resource acquisition proposals subject to section 6(c) review,” BPA concluded that “[[Interregional exchanges are not subject to section 6(c) review.” 51 Fed.Reg. 42902, 42904 (1986).

Petitioners acknowledge that the NTSA is an interregional exchange, Petitioners’ Brief at 23, yet argue that the clear language of the Act compels finding that such an exchange constitutes a major resource acquisition. Petitioners’ Reply Brief at 23. They reason that since section 839d(l) mentions “mutually beneficial interregional exchanges of electric power,” 9 and since section 6(e) review procedures apply to proposals to acquire a major resource under section 839d(l), 10 then a mutually beneficial exchange must constitute a major resource acquisition if it has a planned capability greater than fifty average megawatts and is acquired by the Administrator for more than five years. Id. The problem with this argument is that section 839d(l) does not explicitly define an interregional exchange as a resource acquisition. Rather, it merely authorizes the Administrator to investigate such exchanges. 16 U.S.C. § 839d(l)(2).

BPA followed proper procedures for construing the statute: (1) the language of the statute is ambiguous, (2) the Policy was adopted pursuant to applicable notice and comment procedures; and (3) petitioners did not challenge the policy within the ninety-day limitations period provided for in 16 U.S.C. § 839f(e). Because BPA neither violated any procedural requirements nor construed the statute unreasonably in concluding that the NTSA was not a major resource acquisition, we reject petitioner’s final contention under the NPA.

III.

NEPA

NEPA requires federal agencies to prepare an EIS for “major federal actions *1536 significantly affecting the quality of the human environment.” 42 U.S.C. § 4332 (2)(C). “An agency must prepare an EIS if ‘substantial questions are raised as to whether a project ... may cause significant degradation of some human environmental factor.’” Greenpeace Action v. Franklin, 14 F.3d 1324, 1332 (9th Cir.1992) (quoting LaFlamme v. FERC, 852 F.2d 389, 397 (9th Cir.1988)). NEPA’s goals are “(1) to ensure the agency will have detailed information on significant environmental impacts when it makes its decisions; and (2) to guarantee that this information will be available to a larger audience.” Inland Empire Public Lands v. United States Forest Service, 88 F.3d 754 , 758 (9th Cir.1996). NEPA exists to ensure a process, not a result. Id.

We review BPA’s decision not to prepare an EIS 'under an “arbitrary and capricious” standard of review. Greenpeace Action v. Franklin, 14 F.3d 1324 (9th Cir.1993). Using this standard, we consider only whether BPA’s decision to enter into the NTSAs is based on a “reasoned evaluation of the relevant factors.” Id. at 1332 . We will overturn BPA’s decision only if BPA committed a “clear error in judgment.” Marsh v. Oregon Natural Resources Council, 490 U.S. 360, 378, 385 , 109 S.Ct. 1851, 1861 , 104 L.Ed.2d 377 (1989).

A.

Public Controversy

Petitioners argue that BPA should have prepared an EIS because the decision to enter into the NTSA was extremely controversial. “The existence of a public controversy over the effect of an agency action is one factor in determining whether the agency should prepare [an EIS].” Greenpeace Action, 14 F.3d at 1333 , 40 C.F.R. § 1508.27 (b)(4) (1993). A federal action is controversial if “a substantial dispute exists as to [its] size, nature, or effect.” LaFlamme, 852 F.2d at 400-01 (internal quotations and citations omitted). Controversy does not refer to the existence of opposition to a use. Id. at 401 . While some comments on the preliminary EA expressed concern regarding the NTSAs’ effect on anadromous fish, others suggested as an alternative use that BPA set aside some of the additional storage capacity to benefit fish. BPA addressed the potential effects of the NTSAs on fish in the Fish and Wildlife Agreement, apparently to the satisfaction of some commentators who had expressed concern regarding adverse effects on anadromous fish. The chairman of the Columbia Basin Fish and Wildlife Authority (CBFWA) stated:

BPA’s conclusion that the NTS Fish and Wildlife Agreement alleviated most of the concerns regarding the effect of entering into the NTSA was not arbitrary or capricious. See O.R. at 1504.

B.

Cumulative Impacts

Petitioners also claim that an EIS is required because the EA does not provide an adequate analysis of cumulative impacts resulting from the NTSA, BPA’s 1988 decision to increase the Intertie capacity, 11 and the proposed expansion of the Bureau of Reclamation’s Columbia Basin Project.

Cumulative impact is the impact on the environment which

40 C.F.R. § 1508.7 .

BPA evaluated the cumulative impacts of the NTSA and the Intertie expansion by using computer modeling to update the information in the Intertie EIS with the potential additional impact of the NTSA. When BPA prepared the EA; it made certain assumptions regarding when fish bypasses 12 would be installed at some of the dams. Petitioners charge that BPA ignored information about delays in bypass construction when it determined that the combined effects of the Inter-tie expansion and the NTSA would not significantly affect salmon. BPA replies that the FISHPASS modeling program used in the study is not sensitive to installation dates because it uses a comparative analysis based on assumptions that 'are consistent throughout all studies.

Petitioners may be correct in pointing out that bypass delays could dramatically affect fish survival rates, but BPA is limited in its ability to study the impact of the NTSA by the technology available to it. Petitioners do not suggest how BPA could have adjusted its analyses to account for the discrepancy in installation dates. 13 “NEPA does not require that we decide whether an [environmental assessment] is based on the best scientific methodology available.” Greenpeace Action, 14 F.3d at 1333 . See also Idaho Conservation League, 956 F.2d at 1522.

Petitioners criticize BPA’s method of evaluating the cumulative impacts of the NTSA and the Intertie expansion on individual salmon stocks. BPA performed separate computer analyses to study the impact on salmon of the NTSA alone and of the NTSA together with the Intertie expansion. In one computer model, it simulated hydrosystem operations pursuant to the NTSA. In a second model, it simulated hydrosystem changes resulting from the NTSA and the Intertie expansion. BPA compared these results to a base ease. It then performed detailed assessments on certain stocks for which the FISHPASS model showed specified survival decreases. The purpose of the individual assessments was to determine whether the NTSA-either alone or in conjunction with the Intertie expansion-would significantly affect the survival of salmon stocks that met BPA’s flagging criteria.

Petitioners claim that although BPA individually assessed all stocks that met the flagging criteria under the NTSA model, it did not assess the additional stocks that met the flagging criteria under the cumulative impact model. BPA responds that it did not perform assessments on some of the stocks that showed a potential cumulative impact from the Intertie alone because assessments on those stocks were already included in the Intertie EIS, which BPA considered in the EA. BPA may reasonably incorporate information from an impact analysis for a prior action to evaluate cumulative effects when those effects result exclusively from the prior action. See California Trout v. Schaefer, 58 F.3d 469, 474 (9th Cir.1995) (“[requiring the Corps to duplicate these efforts would be nonsensical”).

Petitioners also argue that BPA should have considered the cumulative impacts of a proposed expansion of the Bureau of Reclamation’s Columbia Basin Project, which would divert more water from the Columbia River for irrigation. With this argument petitioners repeat the same error that guided their equitable treatment argument. Petitioners here focus on how the non-Treaty storage will be allocated. Petitioners worry that if more water is diverted *1538 for irrigation, less water will be left for fish and wildlife. As we discussed in Section II, it is premature for petitioners to challenge how the water will be used. In this case, we review only BPA’s decision to enter into the NTSAs.

The use of the non-Treaty storage will be studied in the Columbia River Hydroelectric Operations System Operation Review (SOR), which was scheduled to be completed in 1994. At the time BPA entered into the NTSAs, BPA and the CBFWA recognized that the use of the non-Treaty storage would be considered in the SOR:

“Non-Treaty Storage Fish and Wildlife Agreement,” (1990) O.R. at 1498. Furthermore, the proposed expansion of the Columbia Basin Project will not escape NEPA review. See California Trout, 58 F.3d at 474 . Indeed, as petitioners recognize, a draft EIS on the Columbia Basin Project was completed in 1989, a year before BPA entered into the NTSAs. Accordingly, we hold that BPA made a “reasoned evaluation of the relevant factors” without considering the proposed expansion of the Columbia River Basin. Greenpeace Action, 14 F.3d at 1332 .

C.

Consideration of Alternatives

NEPA requires that a federal agency “study, develop, and describe appropriate alternatives to recommended courses of action in any proposal which involves unresolved conflicts concerning alternative uses of available resources.” 42 U.S.C. § 4332 (2)(E). See also 40 C.F.R. § 1508.9 (b). “[A]n agency must look at every reasonable alternative, with the range dictated by the nature and scope of the proposed action.” Idaho Conservation League, 956 F.2d at 1520 (internal quotation and citation omitted). ‘We review an agencj’s range of alternatives under a ‘rule of reason’ standard that ‘requires an agency to set forth only those alternatives necessary to permit a reasoned choice.’ ” Headwaters, Inc. v. Bureau of Land Management, 914 F.2d 1174, 1180 (9th Cir.1990) (quoting California v. Block, 690 F.2d 753, 767 (9th Cir.1982)).

Petitioners contend that BPA failed to explore an adequate range of alternatives because it considered only signing the NTSA or doing nothing. They argue that BPA ignored comments that suggested it consider possible uses of non-Treaty storage that would benefit fish, preferring instead to define the objective of its action so specifically as to narrow the reasonable alternatives to its proposed action and no action. We disagree that BPA was required to consider use of non-Treaty storage for fish. The NTSA governs BPA’s rights to storage capacity in Canadian reservoirs, it does not govern the allocation of water stored in those reservoirs. Furthermore, as discussed above, the SOR will address the use of non-Treaty storage capacity, including its use to benefit fish and wildlife. BPA and the CBFWA agreed in the NTS Fish and Wildlife Agreement that the “NTSA will be discussed in the context of the SOR, and that revisions to this Agreement may be necessary and appropriate to implement plans approved appropriate to SOR.” O.R. at 1498. BPA was not required to consider using non-Treaty storage for fish and wildlife at the time it entered into the NTSAs.

D.

Fish and Wildlife Agreement

Petitioners contend that the Administrator was not justified in relying on the NTS Fish and Wildlife Agreement in deciding to proceed with the NTSA, because the *1539 EA does not address this agreement and the public did not have the opportunity to review it during the NTSA public comment process. BPA responds that the agreement was within the range of alternatives the public could have reasonably anticipated. It relies on this court’s statement that “agencies must have some flexibility to modify alternatives canvassed in the draft EIS to reflect public input without having to circulate a supplemental draft EIS describing the proposed action.” Half Moon Bay Fishermans’ Mktg. Ass’n v. Carlucci, 857 F.2d 505, 508-09 (9th Cir.1988) (quotation omitted).

We agree with BPA that it was not necessary to include an analysis of the Fish and Wildlife Agreement in the EA or to allow public comment on the Agreement. Without reference to the Fish' and Wildlife Agreement, the Department of Energy concluded in the FONSI that the NTSA would not result in significant environmental impacts. In deciding to enter into the NTSA, the Administrator relied primarily on the analysis in the EA and the FONSI that the NTSA would have little, if any, effect on anadro-mous fish resources. The Administrator viewed the NTS Fish and Wildlife Agreement as a means of alleviating the concerns of the fisheries community rather than as a means of mitigating environmental impacts. As such, it was a logical outgrowth of the public comment process that the public could have reasonably anticipated. Moreover, many organizations concerned with anadro-mous fish survival participated in negotiating the Agreement, thereby providing significant public input.

CONCLUSION

We deny respondents’ motion to strike petitioners’ supplemental affidavits and the alternative motion for leave to file a supplemental response. We hold that BPA did not violate the Northwest Power Act or NEPA when it entered into the NTSA. Consequently, we will not enjoin BPA from operating the hydrosystem under the NTSA, nor will we remand to BPA for preparation of an EIS.

PETITION FOR REVIEW DENIED.

. Petitioners are Northwest Environmental Defense Center (NEDC), Northwest Resource Information Center (NRIC), Idaho Steelhead and Salmon Unlimited (ISSU), and Salmon for All.

. Bonneville Power Administration (BPA), an agency of the Department of Energy, markets the hydroelectric power generated at a series of dams on the Columbia River and its tributaries.

. The Mid-Columbia is the section of the Columbia River from the Canadian border to its junction with the Snake River.

. The NPA allows the Slates of Idaho, Montana, Oregon, and Washington to each appoint two persons to serve on the Council. 16 U.S.C. § 839b(a)(2).

. The parlies also dispute whether the agreement with BC Hydro violates the United Stales-Canada Columbia River Treaty. At oral argument, petitioners conceded that this issue is not properly before us.

. NEDC submitted the affidavit of its president, Karl Anuta, in which he declares that:

NRIC submitted the affidavit of its executive director, Ed Chaney, in which he declares that:

ISSU submitted the affidavit of its executive coordinator, Mitch Sanchotena, in which he declares that:

Salmon for All submitted the affidavit of Thane Tienson, in which he declares that:

. Petitioners also argue a third basis for injury. They argue that the NTSA Fish Agreement does *1530 not provide for suspending non-Treaty storage operations pursuant to the NTSA in the event of alleged or actual violations of the NTSA Fish Agreement. From this argument, petitioners claim they are currently suffering injury from the agreements because CBFWA has alleged nineteen violations of the Agreement by BPA since 1991. However, because they are challenging only the decision to enter into the agreements, and are not suing for violations of the agreements, we do not consider this ground.

. BPA also cites Marathon Oil Co. v. United States, 807 F.2d 759, 767 (9th Cir.1986), for the proposition that, "[a]s a general rule, we will not consider issues not presented before an administrative proceeding at the appropriate time.” Insofar as Marathon Oil can be read to require exhaustion of administrative remedies before bringing a claim in federal court under section 10(c) of the APA, 5 U.S.C. § 704 , it has been modified by the Supreme Court’s decision in Darby v. Cisneros, 509 U.S. 137 , 113 S.Ct. 2539 , 125 L.Ed.2d 113 (1993) (holding that a court’s authority to require exhaustion of administrative remedies in actions brought under the APA is limited when neither the statute nor agency rules specifically mandate exhaustion as a prerequisite to judicial review).

. Section 839d(l) provides:

16 U.S.C. § 839d(Z)(2).

. Section 6(c) provides, in relevant part:

16 U.S.C. § 839d(c)(l).

. The Intertie is a system of high voltage lines transmitting federal and non-federal power between the Pacific Northwest and the Pacific Southwest. California Energy Comm'n v. Bonneville Power Admin., 909 F.2d 1298 , 1302 (9th Cir.1990).

. A bypass is a structure that allows fish to move through or around a dam without going through the turbines.

. In response to criticisms of the FISHPASS model, BPA stated:

"Non-Treaty Storage Agreement Issue Summary and Response to Comments,” O.R. at 150.