New Jersey v. Delaware

Background

New Jersey brought a boundary dispute with Delaware to this Court about two separate areas: the riverbed within a twelve‑mile circle around New Castle, and the river and bay below that circle. Delaware claimed the entire bed inside the circle up to low‑water mark on the New Jersey side; New Jersey claimed to the middle of the channel. Below the circle, New Jersey argued for the channel (the Thalweg) as the dividing line, while Delaware urged the geographical centre between the shores. A Special Master reported in favor of Delaware for the circle and in favor of New Jersey for the lower river and bay.

Reasoning

For the twelve‑mile circle the Court examined the 1682 feoffment to William Penn, later letters patent of 1683, long possession, and historical acts of government, concluding Delaware’s title to the subaqueous soil within the circle was valid and unbroken. The Court rejected New Jersey’s prescription and acquiescence arguments. For the lower river and bay the Court applied the international‑law principle of the Thalweg: where a well‑defined main ship channel exists, the boundary is the middle of that channel rather than the simple geographical centre.

Real world impact

The judgment gives Delaware ownership of the riverbed inside the twelve‑mile circle up to low‑water mark on the east side and fixes the boundary below the circle at the middle of the main ship channel. The Compact of 1905 remains effective in the ways it preserves concurrent rights. The ruling clarifies which state controls sections of the bed, navigation, fisheries, and related jurisdictional authority.