The Anacostia River / / is a river in the Mid Atlantic region of the United States . It flows from Prince George's County in Maryland into Washington, D.C. , where it joins with the Washington Channel to empty into the Potomac River at Buzzard Point . It is approximately 8.7 miles (14.0 km) long.  The name "Anacostia" derives from the area's early history as Nacotchtank , a settlement of Necostan or Anacostan Native Americans on the banks of the Anacostia River.
Heavy pollution in the Anacostia and weak investment and development along its banks have led to it fitting what a large number of have called "D.C.'s forgotten river." In recent years, however, private organizations, local businesses, and the D.C., Maryland and federal governments have made joint efforts to reduce its pollution levels in order to protect the ecologically valuable Anacostia watershed .
The mainstem of the Anacostia is formed by the confluence of the Northwest Branch and the Northeast Branch just north of Bladensburg, Maryland . Tributaries of these sources include Sligo Creek , Paint Branch , Little Paint Branch, Indian Creek; Upper Beaverdam Creek, Dueling Branch, and Brier's Mill Run. Tributaries of the mainstem Anacostia include Watts Branch , Lower Beaverdam Creek and Hickory Run.
Captain John Smith recorded in his journals that he sailed up the "Eastern Branch" or Anacostia River in 1608 in his search for the main branch of the Potomac River and was well received by the Anacostans. On earlier maps, the river was known as the "Eastern Branch of the Potomac River" until it received its current, official name.
The Washington City Canal operated from 1815 until the mid-1850s, initially connecting the Anacostia to Tiber Creek and the Potomac River; and later to the Chesapeake and Ohio Canal . The city canal fell into disuse in the late nineteenth century, and the city government covered over or filled in various sections. 
During the American Civil War , an extensive line of forts was constructed south of the river in order to prevent Confederate artillery from bombarding the Washington Navy Yard , which lies adjacent to the river.