The Mattaponi River is a 103 miles (165.8 km) tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the York River

York River (Virginia)

The York River is a navigable estuary, approximately long, in eastern Virginia in the United States. It ranges in width from at its head to near its mouth on the west side of Chesapeake Bay. Its watershed drains an area including portions of 17 counties of the coastal plain of Virginia north...

 estuary

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

 in eastern Virginia

Virginia

The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.

It rises as four streams in Spotsylvania County

Spotsylvania County, Virginia

As of the census of 2000, there were 90,395 people, 31,308 households, and 24,639 families residing in the county. The population density was 226 people per square mile . There were 33,329 housing units at an average density of 83 per square mile...

, each of which is given a shorter piece of the Mattaponi's name:

• The Mat River and the Ta River join in Spotsylvania County to form the Matta River;
• The Po River and the Ni River join in Caroline County
  Caroline County, Virginia
  Caroline County is a county located in the Commonwealth of Virginia. As of 2010, the population was 28,545. Its county seat is Bowling Green. Caroline County is also home to The Meadow stables, the birthplace of the renowned racehorse Secretariat, winner of the 1973 Kentucky Derby, Preakness and...
  
   to form the Poni River;
• The Matta River and the Poni River join in Caroline County to form the Mattaponi River.

From the confluence

Confluence (geography)

In geography, a confluence is the meeting of two or more bodies of water. It usually refers to the point where two streams flow together, merging into a single stream...

 of its tributaries, the Mattaponi flows generally southeast through Caroline County, where it collects the South River

South River (Mattaponi River)

The South River is a river in Caroline County in the U.S. state of Virginia. It is a tributary of the Mattaponi River.Rising at the boundary between Caroline County and Spotsylvania County, the South River flows east, passing under U.S. Route 1 and Interstate 95, joining the Mattaponi north of...

; in its lower reaches it defines the boundary between King William

King William County, Virginia

As of the census of 2000, there were 13,146 people, 4,846 households, and 3,784 families residing in the county. The population density was 48 people per square mile . There were 5,189 housing units at an average density of 19 per square mile...

 and King and Queen

King and Queen County, Virginia

As of the census of 2000, there were 6,630 people, 2,673 households, and 1,897 families residing in the county. The population density was 21 people per square mile . There were 3,010 housing units at an average density of 10 per square mile...

 counties. At West Point

West Point, Virginia

West Point is an incorporated town in King William County, Virginia, United States. The population was 2,867 at the 2000 census.-Geography:West Point is located at...

, it meets the Pamunkey River

Pamunkey River

The Pamunkey River is a tributary of the York River, about long, in eastern Virginia in the United States. Via the York River it is part of the watershed of Chesapeake Bay.-Course:...

 to form the York River

York River (Virginia)

The York River is a navigable estuary, approximately long, in eastern Virginia in the United States. It ranges in width from at its head to near its mouth on the west side of Chesapeake Bay. Its watershed drains an area including portions of 17 counties of the coastal plain of Virginia north...

.

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

Sierra Club

The Sierra Club is the oldest, largest, and most influential grassroots environmental organization in the United States. It was founded on May 28, 1892, in San Francisco, California, by the conservationist and preservationist John Muir, who became its first president...

, members of the Mattaponi

Mattaponi

The Mattaponi tribe is one of only two Virginia Indian tribes in the Commonwealth of Virginia that owns reservation land. The larger Mattaponi Indian Tribe lives in King William County on reservation lands that stretch along the borders of the Mattaponi River, near West Point, Virginia.The...

 Indian tribe, and residents of King William County opposing Newport News Waterworks in their efforts to build the King William Reservoir.