The Poquoson River is an 11.7 miles (18.8 km), mostly tidal river in the state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 of 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...

. The river is an arm of Chesapeake Bay

Chesapeake Bay

The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

, entering just south of the mouth 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...

.

The river flows primarily through York County

York County, Virginia

York County is a county located on the north side of the Virginia Peninsula in the Hampton Roads metropolitan area of the Commonwealth of Virginia, a state of the United States. Situated on the York River and many tributaries, the county seat is the unincorporated town of Yorktown...

, rising south of Yorktown

Yorktown, Virginia

Yorktown is a census-designated place in York County, Virginia, United States. The population was 220 in the 2000 census. It is the county seat of York County, one of the eight original shires formed in colonial Virginia in 1634....

 to the west of U.S. Route 17

U.S. Route 17

U.S. Route 17 or U.S. Highway 17 is a north–south United States highway. The highway spans the southeastern United States and is close to the Atlantic Coast for much of its length. The highway's southern terminus is at Punta Gorda, Florida, at an intersection with U.S. Route 41...

 and flowing south to Harwoods Mill Reservoir, where it turns east, flows under Route 17, and becomes tidal. The river flows northeast and becomes the boundary between York County and the city of Poquoson

Poquoson, Virginia

Poquoson is an independent city located on the Virginia Peninsula, in the Hampton Roads metropolitan area of the U.S. state of Virginia. The population was 12,150 according to the 2010 Census...

, reaching Chesapeake Bay just north of Plum Tree Island National Wildlife Refuge

Plum Tree Island National Wildlife Refuge

The Plum Tree Island National Wildlife Refuge is a National Wildlife Refuge in Poquoson, Virginia, located on the southwestern corner of the Chesapeake Bay...

.

The river's name is probably related to pocosin

Pocosin

Pocosin is a term for a type of palustrine wetland with deep, acidic, sandy, peat soils. Groundwater saturates the soil except during brief seasonal dry spells and during prolonged droughts...

.