Washington, D.C. has a total area of 68.3 square miles (177 km2), of which 61.4 square miles (159 km2) is land and 6.9 square miles (18 km2) (10.16%) is water. The District is no longer 100 square miles (260 km2) due to the retrocession of the southern portion of the District back to the Commonwealth of Virginia in 1846. The District's current area consists only of territory ceded by the state of Maryland. Washington is therefore surrounded by the states of Maryland to the southeast, northeast, and northwest and Virginia to the southwest. The District has three major natural flowing streams: the Potomac River, the Anacostia River, and Rock Creek. The Anacostia River and Rock Creek are tributaries of the Potomac.
Contrary to the urban legend, Washington was not built on reclaimed swampland. While wetlands did cover areas along the two rivers and other natural streams, the majority of the District's territory consisted of farmland and tree-covered hills. The highest natural point in the District of Columbia is 409 feet (125 m) above sea level in Tenleytown. The lowest point is sea level at the Potomac River. The geographic center of Washington is located near the intersection of 4th and L Streets NW.
Approximately 19.4% of Washington, D.C. is parkland, which ties New York City for having the largest percentage of parkland among high-density U.S. cities. The U.S. National Park Service manages most of the natural habitat in Washington, D.C., including Rock Creek Park, the Chesapeake and Ohio Canal National Historical Park, the National Mall, Theodore Roosevelt Island, and Anacostia Park. The only significant area of natural habitat not managed by the National Park Service is the U.S. National Arboretum, which is operated by the U.S. Department of Agriculture. The Great Falls of the Potomac River are located upstream (i.e. northwest) of Washington. During the 19th century, the Chesapeake and Ohio Canal, which starts in Georgetown, was used to allow barge traffic to bypass the falls.