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Potomac River

Upper part of the Potomac River


The Potomac River is a tributary of the Chesapeake Bay, located along the mid-Atlantic coast of United States of America (USA). The river is approximately 413 statute miles (665 km) long, with a drainage area of about 14,700 million square miles (38,000 square km). 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 as a whole.


The Potomac River springs from southwest Maryland (MD). The river then forms part of the borders between MD and Washington, DC (the District of Columbia) on the left bank and the State of West Virginia (WV) and the Commonwealth of Virginia (VA) on the right bank. Up to its right bank, the entire Potomac River is considered part of MD, with exception of a small tidal portion within DC.

About 300 miles (483 km) from the source, the Potomac River's estuarine portion commences. About 11 square km of water enters the estuary each year (250 cubic meters/second) at the fall line at Little Falls. Fall line flow is quite variable across months and years, highest during the spring freshet and lowest in late summer (in the absence of hurricanes or major storms).

Once the Potomac drops from the Piedmont to the Coastal Plain, tides further influence the river as it passes through DC 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, MD, and Smith Point, VA, before merging into the Chesapeake Bay.

Major Potomac tributaries include the Shenandoah River (WV and VA) and the Monocacy River (MD) above the fall-line and the Anacostia River (DC and MD) and Occoquan River (VA) below the fall-line.

Over 5 million people live within the Potomac watershed, where precipitation provides the equivalent of over 8 cubic meters (more than 2100 gallons) of water per person per year.


1700 to Present

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, USA's first president, was born in, surveyed and spent most of his life within the Potomac basin. All of DC, the nation's capital city, also lies within the watershed. The 1859 siege of Harper's Ferry along the river's right bank was a precursor to numerous epic battles of the American Civil War in and around the Potomac and its tributaries.

With increasing mining and agriculture upstream and urban sewage and runoff downstream, water quality in 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.

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