The Delaware River Watershed (12,800 square miles) covers parts of New York, Pennsylvania, New Jersey and Delaware. About one-fifth of the upper watershed lies within New York State. These headwaters originate in the Catskill Mountains and eventually flow into Delaware Bay and the Atlantic Ocean.

The Delaware River flows into the Atlantic Ocean. The journey begins in the Catskill Mountains of New York and travels south, forming the border between Pennsylvania and New Jersey, and later between Delaware and New Jersey. As the river reaches the end of its course, it widens significantly to form the Delaware Bay, which is a major estuary covering nearly 800 square miles. This bay serves as a transition zone where the freshwater of the river mixes with the saltwater of the ocean. The river finally empties into the Atlantic Ocean between Cape May, New Jersey, and Cape Henlopen, Delaware. This waterway is of immense economic and ecological importance, serving as a primary shipping channel for the ports of Philadelphia and Wilmington, while also providing critical habitat for horseshoe crabs and migratory shorebirds. For travelers, the mouth of the river marks a popular coastal region famous for its historic lighthouses and expansive Atlantic beaches.