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is normally one for the Federal Government. Report of the Special Master 45 (hereinafter Report). The United States has never opted to draw straight baselines under Article 4. See California II, supra, at 167–169; United States v. Louisiana, 394 U. S. 11, 72-73 (1969) (Louisiana Boundary Case); United States v. Louisiana, 470 U. S. 93, 99 (1985) (Alabama and Mississippi Boundary Case); United States v. Maine, 475 U. S. 89, 94, n. 9 (1986) (Massachusetts Boundary Case). As a variant of its straight baselines argument, Alaska claimed that the United States has historically treated waters between the mainland and fringing islands as "inland waters," so long as the openings between the offlying islands are no more than 10 miles wide. Alaska did not argue that the United States had ever specifically asserted, in its dealings with foreign nations, that the waters of Stefansson Sound are inland waters. Rather, Alaska attempted to identify a general but consistent "10-mile rule" invoked by the United States in its domestic and international affairs. If applied to Alaska's Arctic Coast, the State argued, this rule would require treating the waters of Stefansson Sound as inland waters.

The Master examined the boundary delimitation practices of the United States and concluded that the United States did not have a well-established rule for treating waters between the mainland and fringing islands as inland waters. The Master recognized that, in the Alabama and Mississippi Boundary Case, we suggested that between 1903 and 1961 the United States had "enclos[ed] as inland waters those areas between the mainland and off-lying islands that were so closely grouped that no entrance exceeded 10 geographical miles." 470 U. S., at 106-107. Observing that this statement was not "strictly necessary" to the decision in the Alabama and Mississippi Boundary Case, the Master declined to rely on it here. The Master therefore concluded that, for purposes of measuring Alaska's submerged lands, the State's

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coastline should correspond to a normal baseline under Article 3 of the Convention.

For the reasons discussed below, we find no error in the Master's approach.

A

Under the Convention, a nation's past boundary delimitation practice is relevant in a narrow context: specifically, when a nation claims that certain waters are "historic" inland waters under Article 7(6) of the Convention. If certain geographic criteria are met, Article 7(4) of the Convention permits a nation to draw a "closing line" across the mouth of a bay and to measure its territorial sea outward from that line. Waters enclosed by the line are considered internal waters. Article 7(6) also permits a nation to enclose "historic" bays, even if those waters do not satisfy the geographic criteria of Article 7(4). For a body of water to qualify as a historic bay, the coastal nation "must have effectively exercised sovereignty over the area continuously during a time sufficient to create a usage and have done so under the general toleration" of the community of nations. Id., at 102 (citing Juridical Regime of Historic Waters, Including Historic Bays 56, U. N. Doc. A/CN.4/143 (1962)) (internal quotation marks omitted). Accordingly, where a State within the United States wishes to claim submerged lands based on an area's status as historic inland waters, the State must demonstrate that the United States: (1) exercises authority over the area; (2) has done so continuously; and (3) has done so with the acquiescence of foreign nations. See Alabama and Mississippi Boundary Case, supra, at 101-102.

Recognizing these strict evidentiary requirements, Alaska does not contend that the waters of Stefansson Sound are historic inland waters. Alaska does not purport to show any specific assertion by the United States that the waters of Stefansson Sound are inland waters. Rather, Alaska argues that, at the time it was admitted to the Union, the United States had a general, publicly stated policy of enclosing as

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inland waters areas between the mainland and closely grouped fringing islands. If this general formula is applied to the Alaska's Arctic Coast, the State argues, the waters of Stefansson Sound qualify as inland waters. Alaska maintains that this policy was in effect from the early 1900's to 1971, when the United States published a set of charts strictly applying the arcs-of-circles method to Stefansson Sound. In Alaska's view, relying solely on the Convention's normal baseline approach to delimit the State's submerged lands impermissibly contracts the State's recognized territory from that which existed at the time of statehood.

Since adopting the Convention's definitions to give content to the Submerged Lands Act, we have never sustained a State's claim to submerged lands based solely on an assertion that the United States had adhered to a certain general boundary delimitation practice at the time of statehood. In the Louisiana Boundary Case, we left open the possibility that Louisiana could claim ownership of certain submerged lands by demonstrating a "firm and continuing international policy" of enclosing waters between the mainland and island fringes as "inland waters." 394 U. S., at 74, n. 97. Had that been the United States' "consistent official international stance," the Government "arguably could not abandon that stance solely to gain advantage in a lawsuit to the detriment of Louisiana." Ibid. In that litigation, the State ultimately failed to demonstrate any firm and continuing international policy of enclosing waters behind island fringes as inland waters. See United States v. Louisiana, 420 U. S. 529, 529– 530 (1975) (per curiam) (decree) (accepting Master's recommendation that certain actions by the United States did not establish a general policy of applying straight baselines to near-fringing islands); Report of Special Master in United States v. Louisiana, O. T. 1974, No. 9 Orig., pp. 7-13. Alaska nevertheless claims that in the Alabama and Mississippi Boundary Case the Court identified a "firm and continuing" 10-mile rule for fringing islands. Alaska first contends that

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the Alabama and Mississippi Boundary Case precludes the Government from claiming that the waters of Stefansson Sound are not inland waters. The State then argues in the alternative that independent evidence supports its formulation of the rule. We address Alaska's points in turn.

B

In the Alabama and Mississippi Boundary Case, the Court considered the States' claim that the waters of Mississippi Sound constituted "historic" inland waters under Article 7(6) of the Convention. In discussing whether the States had shown that the United States had continuously asserted the inland water status of Mississippi Sound, the Court identified a general policy "of enclosing as inland waters those areas between the mainland and off-lying islands that were so closely grouped that no entrance exceeded 10 geographical miles." 470 U. S., at 106.

Alaska argues that the Government is estopped from questioning application of this general coastline delimitation practice to its Arctic Coast. Alaska recognizes the rule that the doctrine of nonmutual collateral estoppel is generally unavailable in litigation against the United States, see United States v. Mendoza, 464 U. S. 154, 160-163 (1984), but suggests that the policy considerations underlying this rule do not apply to cases arising under the Court's original jurisdiction, where the Court acts as factfinder and the United States has an incentive to fully litigate all essential issues.

We have not had occasion to consider application of nonmutual collateral estoppel in an original jurisdiction case, and we see no reason to develop an exception to Mendoza here. Even if the doctrine applied against the Government in an original jurisdiction case, it could only preclude relitigation of issues of fact or law necessary to a court's judgment. Montana v. United States, 440 U. S. 147, 153 (1979); Mendoza, supra, at 158. A careful reading of the Alabama and Mississippi Boundary Case makes clear that the Court did

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not attach controlling legal significance to any general delimitation formula.

The Master in that case recited a series of statements and precedents following Mississippi's admission to the Union supporting the view that the Federal Government had treated the waters of Mississippi Sound as inland waters. These statements included multiple references to a rule for closing gulfs, bays, and estuaries with mouths less than 10 miles wide as inland waters, Report of Special Master in Alabama and Mississippi Boundary Case, O. T. 1983, No. 9 Orig., pp. 40, 42, 48-49, 52, and to a rule for closing straits leading to inland waters, id., at 42, 49-50. In addition, the Master cited a 1961 letter from the Solicitor General to the Director of the United States Coast and Geodetic Survey concerning coastline delimitation principles for the Gulf of Mexico, proposing to treat "[w]aters enclosed between the mainland and offlying islands. . . so closely grouped that no entrance exceeds ten miles'" as inland waters. Id., at 52.

In excepting to the Master's conclusion that the waters of Mississippi Sound qualified as historic inland waters, the United States argued that the "generalized... formulations" recited by the Master could not support the States' claim, without evidence of specific federal claims to inland waters status for Mississippi Sound. Exceptions of United States in Alabama and Mississippi Boundary Case, O. T. 1983, No. 9 Orig., pp. 32-33. The Court assumed that the United States' position was correct, but concluded that the States had in fact identified "specific assertions of the status of [Mississippi] Sound as inland waters." 470 U. S., at 107; see id., at 108-110.

In light of the Court's assumption that specific assertions of dominion would be critical to the States' historic title claim, we cannot conclude that any general delimitation policy identified in the Alabama and Mississippi Boundary Case is controlling here. The Court's inquiry in the Alabama and Mississippi Boundary Case was not whether the