New Hampshire v. Maine
The Supreme Court dismissed New Hampshire's lawsuit claiming the entire Piscataqua River and Portsmouth Harbor, ruling that New Hampshire could not now argue the boundary sits on the Maine shore after agreeing in 1977 that it ran through the middle of the river's main navigable channel.
The Court relied on judicial estoppel, a doctrine that stops a party from taking a position in court that flatly contradicts a position it successfully argued in an earlier case, to bar New Hampshire's new claim.
How it got here: New Hampshire filed this as an original action directly in the Supreme Court; Maine responded with a motion to dismiss the complaint.
The Case in Depth
What happened
New Hampshire sued Maine claiming the Piscataqua River boundary runs along the Maine shore, giving New Hampshire the entire river and Portsmouth Harbor, including the Portsmouth Naval Shipyard on Seavey Island. Maine countered that a 1740 royal decree and a 1977 Supreme Court consent judgment already fixed the boundary at the middle of the river's main navigable channel, placing the shipyard in Maine.
The question before the Court
Could New Hampshire now claim the entire Piscataqua River and Portsmouth Harbor after agreeing decades earlier that the boundary ran through the river's main channel?
Why it matters
The ruling keeps the Portsmouth Naval Shipyard on Seavey Island and jurisdiction over shipping in the harbor within Maine's boundary, rather than shifting it to New Hampshire. It also reinforces that even states, not just private litigants, can be held to positions they successfully argued in earlier Supreme Court litigation.
What changes now
The dismissal ends this attempt by New Hampshire to claim the entire Piscataqua River and Portsmouth Harbor. The boundary remains where the 1740 decree and 1977 consent judgment placed it—along the middle of the river's main navigable channel—keeping the Portsmouth Naval Shipyard within Maine's jurisdiction. Because this is a final ruling on the merits of Maine's motion, no further proceedings on this claim are expected.
What this does not decide
The Court did not resolve the parties' competing historical claims about where the 1740 decree's boundary actually falls, and it did not decide the claim-preclusion or issue-preclusion arguments Maine raised. The ruling rests solely on judicial estoppel from New Hampshire's earlier litigation position.
How the Court got there
The legal reasoning, step by step
- The Court applied judicial estoppel, a doctrine that bars a party from taking a position in litigation that clearly contradicts a position it successfully took in an earlier case, protecting the integrity of the judicial process.
- The Court identified the key factors for judicial estoppel: whether the later position is clearly inconsistent with the earlier one, whether the party succeeded in getting a court to accept the earlier position, and whether allowing the change would give that party an unfair advantage.
- The Court found New Hampshire's earlier position in the 1970s litigation—that 'Middle of the River' meant the middle of the main navigable channel—was clearly inconsistent with its new claim that the boundary runs along the Maine shore.
- The Court found New Hampshire had succeeded in getting the 1977 consent judgment adopted on that earlier interpretation and had benefited from it, creating a real risk that accepting the new position would produce inconsistent court determinations.
- The Court rejected New Hampshire's arguments that its earlier position was a mistake or inadvertent, noting New Hampshire had conducted a thorough historical inquiry in the 1970s and had every incentive to argue for a shore boundary then if the evidence supported it.
- The Court concluded that the general reluctance to apply estoppel against government bodies did not apply here, because this dispute was between two states over a boundary rather than a case involving enforcement of law or a change in public policy.
Doctrinal impact
Cases affected by this decision
Reaffirms New Hampshire v. Maine (1976/1977 consent judgment) (426 U.S. 363)
The Court relied on its earlier consent judgment's interpretation of 'Middle of the River' as binding on New Hampshire now.