Concord River

The Concord River is a 16.3-mile-long (26.2 km) tributary of the Merrimack River in eastern Massachusetts in the United States. The river drains a small rural and suburban region northwest of Boston.The river begins in Middlesex County, formed by the confluence of the Sudbury and Assabet rivers at Egg Rock, near the Concord town center. It flows generally north, from eastern Concord (along the northwestern edge of the Boston metropolitan area), joining the Merrimack River from the south on the eastern side of Lowell.