Washington, D.C., in the United States, is located at 38°53′42″N 77°02′11″W / 38.89500°N 77.03639°W / 38.89500; -77.03639 (the coordinates of the Zero Milestone, on the Ellipse). According to the United States Census Bureau, the city has a geographical area of 68.3 square miles (176.9 km2), 61.4 square miles (159.0 km2) of which is land, and the remaining 6.9 square miles (17.9 km2) (10.16%) of which is water.
Washington is surrounded by the states of Virginia (on its southwest side) and Maryland (on its southeast, northeast, and northwest sides); it interrupts those states' common border, which is the south shore of the Potomac River both upstream and downstream from the District. The portion of the Potomac River that passes Washington is virtually entirely within the District's border, as the District extends to the south bank. The city contains the historic "federal city", the territory of which was formerly part of those two adjacent states before they respectively ceded it for the national capital. The land ceded from Virginia was returned by Congress in 1847, so what remains of the modern District was all once part of Maryland.
The topography of the District of Columbia is very similar to the physical geography of much of Maryland. The District has three major natural flowing bodies of water: the Potomac River and two tributaries, the Anacostia River and Rock Creek. The confluence of the Potomac and Anacostia forms the historic peninsula known as Arsenal Point. The District also includes the Washington Channel, which flows into the junction of the Anacostia and Potomac rivers. There are also three man-made reservoirs: Dalecarlia Reservoir, which crosses over the northwest border of the District from Maryland, McMillan Reservoir near Howard University, and Georgetown Reservoir upstream of Georgetown. A fourth, minor reservoir is at Fort Reno in Tenleytown.
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