New Hampshire v. Maine

Background

New Hampshire sued Maine claiming the Piscataqua River and Portsmouth Harbor lie along the Maine shore, seeking control of the river, harbor, and the Portsmouth Naval Shipyard. Maine pointed to a 1740 royal decree and a 1977 consent judgment in which New Hampshire previously agreed that “Middle of the River” meant the river’s main channel, and moved to dismiss the new suit.

Reasoning

The Court asked whether New Hampshire could now assert a position opposite the one it adopted earlier. Applying the equitable rule of judicial estoppel — which prevents a party from taking a position contrary to one it successfully argued before a court — the Court found New Hampshire’s current claim clearly inconsistent, that New Hampshire had benefited from its earlier position, and that allowing the change would unfairly harm Maine. The Court therefore held New Hampshire estopped and granted Maine’s motion to dismiss.

Real world impact

The ruling preserves the settled boundary along the river’s main navigable channel and leaves Seavey Island and the Portsmouth Naval Shipyard under Maine’s control under the prior interpretation. It prevents New Hampshire from reclaiming potentially large areas of land and affects local land development, shipping oversight, and tax authority. The decision enforces finality of the earlier settlement and ends this particular boundary challenge.

Dissents or concurrances

The opinion notes that three Justices had earlier dissented in the 1976 proceedings, calling the consent agreement one of convenience, but the Court previously rejected that view and again enforced the consent interpretation here.