Potomac River

, the Potomac is crossed by the Arlington Memorial Bridge. The Potomac River runs from Fairfax Stone Historical Monument State Park in West Virginia on the Allegheny Plateau to Point Lookout, Maryland, and drains . The length of the river from the junction of its North and South Branches to Point Lookout is . Along the way the following tributaries drain into the Potomac: North Branch Potomac River, South Branch Potomac River, Town Creek, Little Cacapon River, Sideling Hill Creek, Cacapon River, Sir Johns Run, Warm Spring Run, Tonoloway Creek, Fifteenmile Creek, Sleepy Creek, Cherry Run, Back Creek, Conococheague Creek, and Opequon Creek. Lower Potomac River This section covers the Potomac from just above Harpers Ferry in West Virginia down to Little Falls, Maryland on the border between Maryland and Washington, DC. Along the way the following tributaries drain into the Potomac: Antietam Creek, Shenandoah River, Catoctin Creek (Virginia), Catoctin Creek (Maryland), Tuscarora Creek, Monocacy River, Little Monocacy River, Broad Run, Goose Creek, Broad Run, Horsepen Branch, Little Seneca Creek, Tenmile Creek, Great Seneca Creek, Old Sugarland Run, Muddy Branch, Nichols Run, Watts Branch, Limekiln Branch, Carroll Branch, Pond Run, Clarks Branch, Mine Run Branch, Difficult Run, Bullneck Run, Rock Run, Scott Run, Dead Run, Turkey Run, Cabin John Creek, Minnehaha Branch, and Little Falls Branch. Tidal Potomac River on Cobb Island, Charles County, Maryland The Tidal Potomac River lies below the Fall Line. This 108-mile (174-km) stretch encompasses the Potomac from a short distance below the Washington, DC - Montgomery County line, just downstream of the Little Falls of the Potomac River, to the Chesapeake Bay. Along the way the following tributaries drain into the Potomac: Pimmit Run, Gulf Branch, Donaldson Run, Windy Run, Spout Run, Maddox Branch, Foundry Branch, Rock Creek, Rocky Run, Tiber Creek, Roaches Run, Washington Channel, Anacostia River, Four Mile Run, Oxon Creek, Hunting Creek, Broad Creek, Henson Creek, Swan Creek, Piscataway Creek, Little Hunting Creek, Dogue Creek, Accotink Creek, Pohick Creek, Pomonkey Creek, Occoquan River, Neabsco Creek, Powell's Creek, Mattawoman Creek, Chicamuxen Creek, Quantico Creek, Little Creek, Chopawamsic Creek, Tank Creek, Aquia Creek, Potomac Creek, Nanjemoy Creek, Chotank Creek, Port Tobacco River, Popes Creek, Gambo Creek, Clifton Creek, Piccowaxen Creek, Upper Machodoc Creek, Wicomico River, Cobb Island, Monroe Creek, Mattox Creek, Popes Creek, Breton Bay, Leonardtown, St. Marys River, Yeocomico River, Coan River, and Hull Creek. ==History==

Natural history The river itself is at least 3.5 million years old, likely extending back ten to twenty million years before the present when the Atlantic Ocean lowered and exposed coastal sediments along the fall line. This included the area at Great Falls, which eroded into its present form during recent glaciation periods. The stream gradient of the entire river is 0.14%, a drop of 930 m over 652 km. Human history The Potomac River has long been inhabited by Native Americans, including being the periphery of the Delaware Adena culture. Precontact, the region was governed by the Algonquian Piscataway confederacy and their allies as warfare in the region increased. This led to the formation of a more complex political system led by the Tayac with countless Werowances governing local affairs. Their confederacy fractured precontact into smaller werowancies and alliances as power shifted south to the Powhatan confederacy. "Potomac" is a European spelling of Patawomeck, the Algonquian name of a Native American village on its southern bank. Native Americans had different names for different parts of the river, calling the river above Great Falls Cohongarooton, meaning "honking geese" and "Patawomke" below the Falls, meaning "river of swans". In 1608, Captain John Smith explored the river now known as the Potomac and made drawings of his observations which were later compiled into a map and published in London in 1612. This detail from that map shows his rendition of the river that the local tribes had told him was called the "Patawomeck". The spelling of the name has taken many forms over the years from "Patawomeck" (as on Captain John Smith's map) to "Patomake", "Patowmack", and numerous other variations in the 18th century and now "Potomac". The similarity of the name to the Ancient Greek word for river, potamos, has been noted for more than two centuries but it appears to be due to chance. 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. There is an apocryphal legend that Washington threw a silver dollar all the way across the river as a youth (even though the first silver dollar wasn't minted until five years before Washington's death). All of Washington, D.C., the nation's capital city, also lies within the watershed. The First United States Congress by act of July 16, 1790 stated that the nation's capital was to be located on the river. 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, such as the 1861 Battle of Ball's Bluff and the 1862 Battle of Shepherdstown. 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 (September 17, 1862) and Gettysburg (July 1–3, 1863). Confederate General Jubal Early crossed the river in July 1864 on his attempted raid on the nation's capital. The river not only divided the Union from the Confederacy, but also gave name to the Union's largest army, the Army of the Potomac. The Patowmack Canal was intended by George Washington to connect the Tidewater region near Georgetown with Cumberland, Maryland. Started in 1785 on the Virginia side of the river, it was not completed until 1802. Financial troubles led to the closure of the canal in 1830. The Chesapeake and Ohio Canal operated along the banks of the Potomac in Maryland from 1831 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. Washington, D.C. began using the Potomac as its principal source of drinking water with the opening of the Washington Aqueduct in 1864, using a water intake constructed at Great Falls. ==Hydrology==

Water supply and water quality An average of approximately of water is withdrawn daily from the Potomac in the Washington area for water supply, providing about 78 percent of the region's total water usage, this amount includes approximately 80 percent of the drinking water consumed by the region's estimated 6.1 million residents. during the historic 1936 flood. The bridge was so severely damaged by the raging water, and the debris it carried, that its superstructure had to be re-built; the new bridge was opened to traffic in 1939. (This photograph was taken from a vantage point on Glebe Road in Arlington County, Virginia. The houses on the bluffs in the background are located on the Potomac Palisades of Washington, DC.) As a result of damaging floods in 1936 and 1937, Several other dams were proposed for the Potomac and its tributaries. When detailed studies were issued by the Corps in the 1950s, they met sustained opposition, led by U.S. Supreme Court Justice William O. Douglas, resulting in the plans' abandonment. The only dam project that did get built was Jennings Randolph Lake on the North Branch. The Corps built a supplementary water intake for the Washington Aqueduct at Little Falls in 1959. In 1940 Congress passed a law authorizing the creation of an interstate compact to coordinate water quality management among states in the Potomac basin. Maryland, West Virginia, Pennsylvania, Virginia, and the District of Columbia agreed to establish the Interstate Commission on the Potomac River Basin. The compact was amended in 1970 to include coordination of water supply issues and land use issues related to water quality. in the Potomac River is evident from this bright green water in Washington, D.C., caused by a dense bloom of cyanobacteria, April 2012. Beginning in the 19th century, 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 pollution from sewage and restore the beauty and ecology of this historic river. One of the significant pollution control projects at the time was the expansion of the Blue Plains Advanced Wastewater Treatment Plant, which serves Washington and several surrounding communities. Enactment of the 1972 Clean Water Act led to construction or expansion of additional sewage treatment plants in the Potomac watershed. Controls on phosphorus, one of the principal contributors to eutrophication, were implemented in the 1980s, through sewage plant upgrades and restrictions on phosphorus in detergents. On November 13, 2007, the Potomac Conservancy, an environmental group, issued the river a grade of "D-plus", citing high levels of pollution and the reports of "intersex" fish. Since then, the river has improved with a reduction in nutrient runoff, return of fish populations, and land protection along the river. As a result, the group has issued a grade of "B" since 2018. In March 2019, the Potomac Riverkeeper Network launched a laboratory boat dubbed the "Sea Dog", which will be monitoring water quality in the Potomac and providing reports to the public on a weekly basis; in that same month, the catching near Fletcher's Boat House of a Striped Bass estimated to weigh was seen as a further indicator of the continuing improvement in the health of the river. On January 19, 2026, a large sewage pipe, the Potomac Interceptor, ruptured near Lock 10 of the C&O Canal and the Clara Barton Parkway, causing a spill of 300 million gallons into the river. (The interceptor sewer originates in the Virginia and Maryland suburbs. One section of the system runs in a reinforced concrete pipe next to the canal, and transports wastewater to the Blue Plains Advanced Wastewater Treatment Plant in Washington.) The contamination from the spill is thousands of times higher than what is considered safe for human use. Work has been done to redirect the sewage into a contained part of the canal. Discharge File:Potomac River Discharge at Little Falls 1931-2017.jpg|thumb|left|This chart displays the Annual Mean Discharge of the Potomac River measured at Little Falls, Maryland for Water Years 1931–2017 (in cubic feet per second). Source of data: USGS. however, the most damaging flood to affect Washington, DC and its metropolitan area was that of October 1942. ==Legal issues==

For 400 years Maryland and Virginia have disputed control of the Potomac and its North Branch since both states' original colonial charters grant the entire river rather than half of it as is normally the case with boundary rivers. In its first state constitution adopted in 1776, Virginia ceded its claim to the entire river but reserved free use of it, an act disputed by Maryland. Both states acceded to the 1785 Mount Vernon Compact and the 1877 Black-Jenkins Award which granted Maryland the river bank-to-bank from the low-water mark on the Virginia side while permitting Virginia full riparian rights short of obstructing navigation. From 1957 to 1996, the Maryland Department of the Environment (MDE) routinely issued permits applied for by Virginia entities concerning the use of the Potomac. However, in 1996 the MDE denied a permit submitted by the Fairfax County Water Authority to build a water intake offshore, citing potential harm to Maryland's interests by an increase in Virginia sprawl caused by the project. After years of failed appeals within the Maryland government's appeal processes, in 2000 Virginia took the case to the Supreme Court of the United States, which exercises original jurisdiction in cases between two states. Maryland claimed Virginia lost its riparian rights by acquiescing to MDE's permit process for 63 years (MDE began its permit process in 1933). A Special Master appointed by the Supreme Court to investigate recommended the case be settled in favor of Virginia, citing the language in the 1785 Compact and the 1877 Award. On December 9, 2003, the Court agreed in a 7–2 decision. The original charters are silent as to which branch from the upper Potomac serves as the boundary, but this was settled by the 1785 Compact. When West Virginia seceded from Virginia in 1863, the question of West Virginia's succession in title to the lands between the branches of the river was raised, as well as title to the river itself. Claims by Maryland to West Virginia land north of the South Branch (all of Mineral and Grant Counties and parts of Hampshire, Hardy, Tucker and Pendleton Counties) and by West Virginia to the Potomac's high-water mark were rejected by the Supreme Court in two separate decisions in 1910. == Fauna ==

Fish A variety of fish inhabit the Potomac, including bass, muskellunge, pike, walleye. The northern snakehead, an invasive species resembling the native bowfin, lamprey, and American eel, was first seen in 2004. Many species of sunfish are also present in the Potomac and its headwaters. Although rare, bull sharks can be found. After having been depressed for many decades, the river's population of American shad is currently re-bounding as a result of the ICPRB's successful "American Shad Restoration Project" that was begun in 1995. In addition to stocking the river with more than 22 million shad fry, the Project supervised the construction of a fishway that was built to facilitate the passage of adults around the Little Falls Dam on the way to their traditional spawning grounds upstream. Mammals Early European colonists who settled along the Potomac found a diversity of large and small mammals living in the dense forests nearby. Bison, elk, wolves (both gray and red) and cougars were still present at that time, but had been hunted to extirpation by the middle of the 19th century. Among the denizens of the Potomac's banks, beavers and otters met a similar fate, while small populations of American mink and American martens survived into the 20th century in some secluded areas. There is no record of early settlers having observed marine mammals in the Potomac, but several sightings of Atlantic bottle-nosed dolphins (Tursiops truncatus) were reported during the 19th century. In July 1844, a pod of 14 adults and young was followed up the river by men in boats as high as the Aqueduct Bridge (approximately the same location occupied by Key Bridge today). Since 2015, perhaps as a result of warmer temperatures, rising water levels in the Chesapeake Bay and improving water quality in the Potomac, unprecedented numbers of Atlantic bottle-nosed dolphins have been observed in the river. According to Dr. Janet Mann of Georgetown University's Potomac-Chesapeake Dolphin Project, more than 500 individual members of the species have been identified in the Potomac during this period. Birds Reptiles s are frequently spotted along the towpath of the C&O Canal. Amphibians ==See also==