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. history, it was the scene of an important early battle of the American Revolutionary War and was the subject of a famous 19th-century book by Henry David Thoreau. Description and early history 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. It is a gently flowing stream with little variation in topography along most of its route. Its drainage basin stretches into Worcester County and includes 36 towns within Massachusetts. Native Americans called it the Musketaquid or "grass-grown" river because of its sluggish waters abound in aquatic or semi-aquatic vegetation and its banks are fringed with wild grasses and sedges which stretch for miles along both sides of this placid stream. This creates a good environment for a variety of fish, including bass, shad, and alewife (river herring), pickerel, carp, and American eel. Native Americans wove sticks in intricate designs to trap Alewives and other migrating fish at the mouths of rivers throughout this region. By 1635, settlers from England began to arrive, and they gave the river its present name. On April 19, 1775, the Old North Bridge over the river in the town of Concord was famously the scene of the Battle of Concord (on the same day when the first shots of the Revolutionary War were fired at nearby Lexington). The current version of the bridge (a reproduction) is preserved by the National Park Service. Henry David Thoreau wrote his first book, A Week on the Concord and Merrimack Rivers, in 1849 while living at nearby Walden Pond. His book recounted a seven-day boat trip on the rivers with his brother John, who had since died. Thoreau recounted his exploration of the natural beauty of the river, and his accompanying thoughts on such eternal themes as truth, poetry, travel, and friendship. Despite the growth of the suburbs in the vicinity of the river, it remains a popular canoeing destination today. The last mile of the