The Sudbury River is a 32.7 miles (52.6 km) tributary of the Concord River

Concord River

The Concord River is a tributary of the Merrimack River in eastern Massachusetts in the United States. The river drains a small rural and suburban region northwest of Boston. One of the most famous small rivers in U.S...

 in Middlesex County, Massachusetts

Middlesex County, Massachusetts

-National protected areas:* Assabet River National Wildlife Refuge* Great Meadows National Wildlife Refuge* Longfellow National Historic Site* Lowell National Historical Park* Minute Man National Historical Park* Oxbow National Wildlife Refuge...

, in the United States.

Originating in the Cedar Swamp in Westborough, Massachusetts

Westborough, Massachusetts

Westborough is a town in Worcester County, Massachusetts, United States. The population was 18,272 at the 2010 census. The town is governed under the New England open town meeting system, headed by a five member elected Board of Selectmen whose duties include licensing, appointing various...

, near the boundary with Hopkinton

Hopkinton, Massachusetts

Hopkinton is a town in Middlesex County, Massachusetts, just under 30 miles west and south of Boston. The town is best known as the starting point of the Boston Marathon, held annually on Patriots' Day in April, and as the home of computer storage firm EMC Corporation.For geographic and demographic...

, it meanders generally northeast to its confluence

Confluence

Confluence, in geography, describes the meeting of two or more bodies of water.Confluence may also refer to:* Confluence , a property of term rewriting systems...

 with the Assabet River

Assabet River

The Assabet River is a small river about west of Boston, Massachusetts. The river is long. The , headquartered in West Concord, Massachusetts, is a non-profit organization dedicated to the preservation, protection, and enhancement of the natural and recreational features of the Assabet River and...

 at Egg Rock

Egg Rock

Egg Rock is an outcrop of Silurian Straw Hollow Diorite at the confluence of the Assabet and Sudbury rivers, where they form the Concord River in Concord, Massachusetts. The outcrop is located on a roughly oval intermittent island of about 100 by 50 meters...

 in Concord, Massachusetts

Concord, Massachusetts

Concord is a town in Middlesex County, Massachusetts, in the United States. As of the 2010 census, the town population was 17,668. Although a small town, Concord is noted for its leading roles in American history and literature.-History:...

, to form the Concord River

Concord River

The Concord River is a tributary of the Merrimack River in eastern Massachusetts in the United States. The river drains a small rural and suburban region northwest of Boston. One of the most famous small rivers in U.S...

. It has a 162 square miles (419.6 km²) drainage area.

On April 9, 1999, nearly 17 miles (27.4 km) of the river were "recognized for their outstanding ecology, history, scenery, recreation values, and place in American literature," by being designated as a part of the National Wild and Scenic Rivers System. The 14.9 miles (24 km) segment of the Sudbury River beginning at the Danforth Street Bridge in the town of Framingham

Framingham, Massachusetts

Framingham is a New England town in Middlesex County, Massachusetts, United States. The population was 68,318 as of the United States 2010 Census. -History:...

, downstream to the Route 2 bridge in Concord, is designated as a Scenic River, and the 1.7 miles (2.7 km) segment from the Route 2 bridge downstream to its confluence with the Assabet River at Egg Rock is designated as a Recreational River, along with adjoining stretches of the Assabet and Concord rivers.

Mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 contamination was discovered in the 1970s from the Nyanza plant in Ashland

Ashland, Massachusetts

Ashland is a town in Middlesex County, Massachusetts, United States. It is part of the MetroWest region. The population was 16,593 at the 2010 census.-History:...

. The EPA subsequently listed the town as a toxic site and led a clean up effort to repair the damage. It is still recommended that fish caught downriver not be eaten.