The Potomac River flows into the Chesapeake Bay, located along the mid-Atlantic coast of the United States. The river is approximately 383 statute miles (616 km) long, with a drainage area of about 14,700 square miles (38,000 km²). In terms of area, this makes the Potomac River the fourth largest river along the Atlantic coast of the USA and the 21st largest in the USA. Over 5 million people live within the Potomac watershed, where precipitation provides the equivalent of over 8 m³ (more than 2,100 US gallons) of water per person per year. The river forms part of the borders between Maryland and Washington, D.C. on the left descending bank and West Virginia and Virginia on the river's right descending bank. The entire lower Potomac River is part of the State of Maryland, with the exception of a small tidal portion within the District of Columbia. Except for a small portion of its headwaters in West Virginia, the North Branch Potomac River is considered part of Maryland to the low water mark on the opposite bank. The South Branch Potomac River lies completely within the state of West Virginia except for its headwaters, which lie in Virginia. The Potomac River runs 383 miles (616 km) from the Fairfax Stone in West Virginia to Point Lookout, Maryland and drains 14,679 square miles (38,020 km2). The average flow is 10,800 ft³/s (306 m³/s). The largest flow ever recorded on the Potomac at Washington, D.C. was in March 1936 when it reached 425,000 ft³/s (12,000 m³/s). The lowest flow ever recorded at the same location was 600 ft³/s (17 m³/s) in September 1966. An average of approximately 486 million gallons of water per day (21 m³/s) is withdrawn daily in the Washington area for water supply. The river has two sources. The source of the North Branch is at the Fairfax Stone located at the junction of Grant, Tucker, Preston counties in West Virginia. The source of the South Branch is located near Hightown in northern Highland County, Virginia. The river's two branches converge just east of Green Spring in Hampshire County, West Virginia to form the Potomac. Once the Potomac drops from the Piedmont to the Coastal Plain, tides further influence the river as it passes through Washington, D.C. and beyond. Salinity in the Potomac River Estuary increases thereafter with distance downstream. The estuary also widens, reaching 11 statute miles (17 km) wide at its mouth, between Point Lookout, Maryland and Smith Point, Virginia before flowing into the Chesapeake Bay. "Potomac" is a European spelling of an Algonquian name for a tribe subject to the Powhatan confederacy, that inhabited the upper reaches of the Northern Neck in the vicinity of Fredericksburg. Some accounts say the name means "place where people trade" or "the place to which tribute is brought". The natives called the river above the falls Cohongarooton, translated as "river of geese", and that area was renowned in early years for an abundance of both geese and swans. The spelling of the name has been simplified over the years from "Patawomeke" (as on Captain John Smith's map) to "Patowmack" in the 18th century and now "Potomac". Some scholars have also suggested it is rooted in the ancient Greek for river, "potamos", blended with the Powhatan name "Patawomeke". The river's name was officially decided upon as Potomac by the Board on Geographic Names in 1931. The Potomac River brings together a variety of cultures throughout the watershed from the coal miners of upstream West Virginia to the urban residents of the nation's capital and, along the lower Potomac, the watermen of Virginia's Northern Neck.
Being situated in an area rich in American history and American heritage has led to the Potomac being nicknamed "the Nation's River." George Washington, the first President of the United States, was born in, surveyed, and spent most of his life within the Potomac basin. All of Washington, D.C., the nation's capital city, also lies within the watershed. The 1859 siege of Harper's Ferry at the river's confluence with the Shenandoah was a precursor to numerous epic battles of the American Civil War in and around the Potomac and its tributaries. General Robert E. Lee crossed the river, thereby invading the North and threatening Washington, D.C. twice in campaigns climaxing in the battles of Antietam and Gettysburg. The Patowmack Canal was intended by George Washington to connect the Tidewater near Georgetown with Cumberland, Maryland. Started in 1785, it was not completed until 1802. Financial troubles closed the canal in 1830. The Chesapeake and Ohio Canal operated along the banks of the Potomac in Maryland from 1850 to 1924 and also connected Cumberland to Washington, D.C. This allowed freight to be transported around the rapids known as the Great Falls of the Potomac River, as well as many other, smaller rapids. With increasing mining and agriculture upstream and urban sewage and runoff downstream, the water quality of the Potomac River deteriorated. This created conditions of severe eutrophication. It is said that President Abraham Lincoln used to escape to the highlands on summer nights to escape the river's stench. In the 1960s, with dense green algal blooms covering the river's surface, President Lyndon Johnson declared the river "a national disgrace" and set in motion a long-term effort to reduce sewage pollution and restore the beauty and ecology of this historic river. By the end of the 20th century, there was notable success, as massive algal blooms vanished and recreational fishing and boating rebounded. Still, the aquatic habitat of the Potomac River and its tributaries remain vulnerable to eutrophication, heavy metals, pesticides and other toxic chemicals, over-fishing, alien species, and pathogens associated with fecal coliform bacteria and shellfish diseases. On November 13, 2007, environmental group the Potomac Conservancy issued the river a grade of "D-plus", citing high levels of pollution and reports of "intersex" fish. The Potomac was designated as one of the American Heritage Rivers in 1997.
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