The Delaware River is a river on the Atlantic coast of the United States. The Delaware was explored by Adriaen Block as part of the New Netherlands Colony, and was named the South River to mark the southernmost reach of that colony.
The river meets tide-water at Trenton, New Jersey. Its total length, from the head of the longest branch to the capes, is 410 miles (660 km), and above the head of the bay its length is 360 miles (579 km). The mean freshwater discharge of the Delaware River into the estuary is 11,550 cubic feet (330 m³) per second.
The Delaware River constitutes in part the boundary between Pennsylvania and New York, the entire boundary between New Jersey and Pennsylvania, and most of the boundary between Delaware and New Jersey. A historical oddity, the Delaware-New Jersey Border is actually at the eastern-most river shoreline within the Twelve-Mile Circle of New Castle, rather than the usual mid river or mid channel borders, causing small portions of the New Jersey peninsula falling west of the shoreline to fall under the jurisdiction of Delaware. The rest of the borders follow a mid-channel approach.
Commerce was once important on the upper river, primarily prior to railway competition (1857).
The mean tides below Philadelphia are about . The magnitude of the commerce of Philadelphia has made the improvements of the river below that port of great importance. Small improvements were attempted by Pennsylvania as early as 1771.
In the "project of 1885" the United States government undertook systematically the formation of a 26 ft (8 m) channel 600 ft (180 m) wide from Philadelphia to deep water in Delaware Bay. The River and Harbor Act of 1899 provided for a 30 foot (9 m) channel 600 feet (180 m) wide from Philadelphia to the deep water of the bay.
