Watershed Management Area 9 (WMA09) covers the main stem of the Raritan River, the South River, and the Lawrence Brook. The main stem of the Raritan spans from the confluence of the North Branch and the South Branch to the Raritan Bay. The watershed includes parts of Middlesex, Somerset, and Monmouth counties. Land use in the main stem Raritan River watershed is primarily urban and suburban, with industrial and commercial centers throughout. The South River begins in Spotswood and flows into the Raritan River at Sayreville. Land use in the upper part of this area is primarily agricultural and forested. New industrial and residential development is rising in these areas, as well as existing, older development in the South River subwatershed. Construction activities, increased use of impervious surfaces and stream bank modification have all contributed to stilt loads and local flooding. There is an increasing amount of runoff from urban services, roads, and storm sewers. These conditions have reduced water quality and fish habitat.

Wildlife in WMA09 can be characterized by its wide variety of bird species, including the American Oystercatcher, Bald Eagle, Osprey, Peregrine Falcon, and a wide range of gulls. A shad fishery is developing in the Raritan, fostered by dam removals. Improvements in water quality have brought the return of many fish populations to the lower Raritan, including largemouth and smallmouth bass, carp, yellow perch, sunfish, catfish, and American eel.

The key environmental organizations working in WMA09 are the Lawrence Brook Watershed Partnership and the Lower Raritan Watershed Partnership.  Researchers from the School of Environmental and Biological Science are involved in fish tagging, oyster restoration, and water quality concerns including a water quality data project and a green infrastructure project focused on reducing impervious surfaces that contribute to area flooding.