The Assunpink as well as the Nishisawick, Lockatong, Wickecheoke and Alexsaoken Creeks all flow directly into the Delaware River. The Assunpink Creek drains an area of 91 square miles. It is about 25 miles long, flowing from Millstone Township in Monmouth County through central Mercer County to the Delaware River at Trenton. Shabakunk Creek and Miry Run are the major tributaries to the Assunpink. A number of impoundments exist along Assunpink Creek and its tributaries for flood control and other purposes.
Population is centered in Trenton and surrounding areas.
Water quality at Trenton is poor. Nutrients are elevated, sanitary quality is very poor and the water seems to have excessive copper and lead. Crop production in the upstream sections of the Assunpink is known to have led to soil erosion and stream siltation. Farther downstream, agriculture gives way to urban runoff as the principal source of nonpoint source contamination, specifically land development and urban runoff. In Trenton, however, water quality degradation is evident from the large municipal and industrial wastewater contributions to the creek.