Delaware River. The Delaware River is a major river on the Atlantic coast of the United States. It drains an area of 14,119 square miles in five U.S. states: Delaware, Maryland, New Jersey, New York, Pennsylvania. Rising in two branches in New York state's Catskill Mountains, the river flows 419 miles into Delaware Bay where its waters enter the Atlantic Ocean near Cape May in New Jersey and Cape Henlopen in Delaware. Not including Delaware Bay, the river's length including its two branches is 388 miles.The Delaware River is one of nineteen Great Waters recognized by the America's Great Waters Coalition. The Delaware River rises in two main branches that descend from the western flank of the Catskill Mountains in New York. The West Branch begins near Mount Jefferson in the Town of Jefferson in Schoharie County. The river's East Branch begins at Grand Gorge near Roxbury in Delaware County. These two branches flow west and merge near Hancock in Delaware County, and the combined waters flow as the Delaware River south. Through its course, the Delaware River forms the boundaries between Pennsylvania and New York, the entire boundary between New Jersey and Pennsylvania, and most of the boundary between Delaware and New Jersey. The river meets tide-water at the junction of Morrisville, Pennsylvania, and Trenton, New Jersey, at the Falls of the Delaware. The river's navigable, tidal section served as a conduit for shipping and transportation that aided the development of the industrial cities of Trenton, Camden, and Philadelphia.