The Delaware River Basin occupies an area of 12,765 square miles, in portions of south central New York, northeast Pennsylvania, northeast Delaware, and western New Jersey (fig. 1). The river begins as two streams in the Catskill Mountains, the East and West Branches. The two tributaries flow in a southwesterly direction until they meet at Hancock, N.Y. The length of the river from the mouth of Delaware Bay to the confluence at Hancock is 331 miles. Approximately 200 miles of the river between Hancock, N.Y., and Trenton, N.J., is nontidal.