New Hampshire and Maine share a border that runs from northwest to southeast. At the borders southeastern end, New Hampshires easternmost point meets Maines southernmost point. The boundary in this region follows the Piscataqua River eastward into Portsmouth Harbor and, from there, extends in a southeasterly direction into the sea. In 1977, in a dispute between the two States over lobster fishing rights, this Court entered a consent judgment setting the precise location of the States "lateral marine boundary," i.e., the boundary in the marine waters off the coast, from the closing line of Portsmouth Harbor five miles seaward. New Hampshire v. Maine, 426 U. S. 363; New Hampshire v. Maine, 434 U. S. 1, 2. The Piscataqua River boundary was fixed by a 1740 decree of King George II at the "Middle of the River." See 426 U. S., at 366-367. In the course of litigation, the two States proposed a consent decree in which they agreed, inter alia, that the descriptive words "Middle of the River" in the 1740 decree refer to the middle of the Piscataqua Rivers ma