natural region in eastern Virginia, U.S., comprising a low-lying alluvial plain (floodplain) on the western shore of Chesapeake Bay between the Atlantic Ocean and the fall line (a line marking the junction between the hard rocks of the Appalachians and the softer deposits of the coastal plain). It is crossed by the Potomac (Potomac River), Rappahannock (Rappahannock River), York, and James (James River) rivers and their tidal estuaries. The Great Dismal Swamp, astride the boundary with North Carolina to the south, is a distinctive feature. The first English settlements in America were founded in the Tidewater region, beginning with Jamestown (Jamestown Colony) in 1607.