The Mattaponi River is a 103-mile-long (166 km)[1] tributary of the York River estuary in eastern Virginia in the United States.
It rises as four streams in Spotsylvania County, each of which is given a shorter piece of the Mattaponi's name:
From the confluence of its tributaries, the Mattaponi flows generally southeast through Caroline County, where it collects the South River; in its lower reaches it defines the boundary between King William and King and Queen counties. At West Point, it meets the Pamunkey River to form the York River.
Over the past few years, residents of the counties surrounding Mattaponi River have hotly debated a proposed reservoir, with environmental groups such as the Sierra Club, members of the Mattaponi Indian tribe, and residents of King William County opposing Newport News Waterworks in their efforts to build the King William Reservoir.