The watershed management area includes watersheds draining the central western portion of New Jersey in Hunterdon and Mercer Counties. The Assunpink as well as the Nishisawick, Lockatong, Wickecheoke and Alexsaoken Creeks all flow directly into the Delaware River. The area lies mostly in Hunterdon and Mercer Counties and includes the following watersheds: Assunpink Creek and Lockatong Creek

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. Land uses in this watershed are both agricultural/undeveloped and urban/suburban. 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.

The tributaries to this 45 mile length of the Delaware River include Hakihokake, Harihokake, Nishisakawick, Lockatong, Wickecheoke, Alexauken, and Swan Creeks in Hunterdon County, and Moores, Fiddlers, and Jacobs Creeks in Mercer County. There are no large population centers here, but smaller towns are Milford Borough, Frenchtown, Sergeantsville, Lambertville and Stockton. Two impoundments are the Swan Creek Reservoirs, East and West. The land use in this area is primarily agricultural and forested, with residential and commercial development scattered throughout. Residential development is increasing in these small watersheds.

The last of the ambient physical/chemical monitoring stations within this region was discontinued in 1991. Monitoring now is limited to biological assessments. Prior to 1991 and throughout the latter half of the 1980s, Wickecheoke Creek at Stockton was the only ambient monitoring station on the Delaware River tributaries between the Musconetcong River and the Assunpink Creek. Wickecheoke Creek, based upon its last ambient monitoring assessment had good overall water quality, with conditions degrading to fair in mid-summer. Water quality problems observed were elevated stream temperatures in warm weather periods and excessive levels of total nitrogen. Some limited violations (7 percent) of State criteria for fecal coliform were recorded, yet the geometric mean for the last period of assessment (68 MPN/100 ml) was low.

Locatcong and Wickecheoke Creeks are impacted by runoff from crop land and from pasture land. These agricultural sources are believed to be on the decline and are being replaced by increasing quantities of runoff from road construction/maintenance. These streams also receive occasional septic tank leachate which is suspected to have contributed to nutrient enrichment and fecal coliform contamination.