It 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 main, west or Mohawk branch rises in Schoharie county, N.Y., about 1886 feet (575 m) above the sea, and flows tortuously through the plateau in a deep trough until it emerges from the Catskills. Other branches rise in Greene and Delaware counties.
In the upper portion of its course the varied scenery of its hilly and wooded banks is exquisitely beautiful. After leaving the mountains and plateau, the river flows down broad Appalachian valleys, skirts the Kittatinny range, which it crosses at the Delaware Water Gap, between nearly vertical walls of sandstone, and passes through a quiet and charming country of farm and forest, diversified with plateaus and escarpments, until it crosses the Appalachian plain and enters the hills again at Easton, Pa. From this point it is flanked at intervals by fine hills, and in places by cliffs, of which the finest are the Hockamixon Rocks, 3 miles (5 km) long and above 200 feet (60 m) high.
At Trenton there is a fall of 8 feet (2.4 m). Below Trenton the river becomes a broad, sluggish inlet of the sea, with many marshes along its side, widening steadily into its great estuary, Delaware Bay.
Its main tributaries in New York are Mongaup and Neversink rivers and Callicoon Creek ; from Pennsylvania, Lackawaxen, Lehigh, and Schuylkill rivers; and from New Jersey, Rancocas Creek and Musconetcong and Maurice rivers. Oldmans and Raccoon creeks are tributaries in New Jersey.
Commerce was once important on the upper river, but only before the beginning of railway competition (1857). The Delaware division of the Pennsylvania Canal, running parallel with the river from Easton to Bristol, was opened in 1830. A canal from Trenton to New Brunswick, called the Delaware & Raritan Canal, unites the waters of the Delaware and Raritan rivers; the Morris and the Delaware and Hudson canals connect the Delaware and Hudson rivers; and the Chesapeake and Delaware Canal joins the waters of the Delaware with those of the Chesapeake Bay.
The mean tides below Philadelphia are about 6 feet. 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.
- Benjamin Franklin Bridge
- Betsy Ross Bridge
- Burlington-Bristol Bridge
- Commodore Barry Bridge
- Delaware Memorial Bridge
- Scudders Falls Bridge
- Tacony-Palmyra Bridge
- Trenton Toll Bridge
- Walt Whitman Bridge
- Burlington County Bridge Commission
- Delaware River Joint Toll Bridge Commission
- Delaware River Port Authority
- Washington Crossing