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General Facts & FAQs

The Potomac basin stretches across parts of four states (Maryland, Pennsylvania, Virginia and West Virginia)Antietam Creek at Burnside Bridge as well as the District of Columbia. This area is also called the Potomac watershed. It includes all of the land area where water drains towards the mouth of the Potomac - the point where the river spills into the Chesapeake Bay. The land of the Potomac Basin varies a great deal from its sources to its mouth, and so do its people. It is difficult to fully describe the Potomac and its people because of their variety and because they are both constantly changing. With that in mind, here is a current snapshot of the basin's land, its people and its water.


The drainage area of the Potomac includes 14,670 square miles in four states: Virginia (5,723 sq. mi.), Maryland (3,818 sq. mi.), West Virginia (3,490 sq. mi.), Pennsylvania (1,570 sq. mi.), and the District of Columbia (69 sq. mi.). The basin's total area varies depending on map projection used.

The basin lies in five geological provinces: the Appalachian Plateau, the Ridge and Valley, Blue Ridge, Piedmont Plateau, and Coastal Plain.

The Potomac meanders over 383 miles from Fairfax Stone, West Virginia to Point Lookout, Maryland. The river's distance will vary with map projection and location of measuring tool in the river (ie. middle of river, Maryland shoreline, Virginia shoreline).

The majority of the basin's land area is covered by forests at 57.6 percent of the land area. Developed land makes up 4.8% percent of the basin's land area, while agriculture cover 31.8 percent. Water and wetlands make up five percent of the basin's land area.

The Potomac's major tributaries include: the Anacostia River, Antietam Creek, the Cacapon River, Catoctin Creek, Conocoheague Creek, the Monocacy River, the North Branch, the South Branch, the Occoquan River, the Savage River, the Senaca Creek, and the Shenandoah River. Visit our maps section to see these watersheds in detail. 


The population of the basin is approximately 6.11 million (2010 estimated census). The population has increased by about five percent since 2005.

The following information is based on 2010 estimated census data.

Jurisdiction Population in Basin by Jurisdiction Population Density per Square Mile
Virginia 2,807,871 490
Maryland 2,237,745 586
West Virginia 262,596 75
Pennsylvania 200,675 128
Washington, D.C. 602,723 8,735

The national average population density is 84 people per square mile and in the late 1500s the average population density was 2.2 people per square mile.

People living in urban areas account for the lion's share of the basin's residents at almost 81 percent of the population. Those living in rural areas make up 18.6 percent of the population, while those living on farms account for .7 percent.

The Washington metropolitan area has approximately 5.36 million residents or almost three-quarters of the basin's population.

Major cities in the Potomac basin include: Bethesda, Cumberland, Hagerstown, Frederick, Rockville, Waldorf, and St. Mary's City in Maryland, Chambersburg and Gettysburg in Pennsylvania, Alexandria, Arlington, Harrisonburg, and Front Royal in Virginia, Harper's Ferry, Charles Town, and Martinsburg in West Virginia, and the largest city in the basin, Washington, D.C.

The basin's major industries include: agriculture and forestry throughout the basin, coal mining and pulp and paper production along the North Branch Potomac River; chemical production and agriculture in the Shenandoah valley; high-tech, service, and light industry, as well as military and government installations in the Washington metropolitan area; and fishing in the lower Potomac estuary.


The largest flow ever recorded on the Potomac at Washington, D.C., was 275 billion gallons per day in March 1936. The lowest flow ever recorded at the same location was 388 million gallons per day in September 1966. The average flow at this location is about 7 billion gallons per day. These figures are all before water supply withdrawals.

An average of approximately 486 million gallons of water is withdrawn daily in the Washington area for water supply. Approximately 100 million gallons per day of ground water used in rural areas.

Almost 86 percent of the basin's population receives its drinking water from public water suppliers while 13 percent uses well water.

Public water treatment plants treat approximately 83 percent of the basin's waste water. Another 16 percent is treated by private septic systems.

Jump to the Potomac Timeline

The Nature Conservancy's 10 Things You Should Know About the Nation's River" interactive map.

ICPRB Seeks Watershed Coordinator

aerial suburbia

The Interstate Commission on the Potomac River Basin (ICPRB), a small quasi-governmental agency that advises the Potomac jurisdictions on water quality and resources issues, is hiring a Watershed Coordinator. The Watershed Coordinator leads ICPRB efforts to encourage water quality and related improvements through increased public involvement and stewardship. The coordinator provides support for local governments and community based watershed organizations focused on improving water quality and river health throughout the Potomac basin. Learn more!

Look at the Potomac’s Big Mussels!

LampsilusMusselThe ICPRB is surveying freshwater mussel populations in the Potomac as part of a multi-year project with the U.S. Geological Survey and Maryland Department of Natural Resources. This picture was taken by Living Resources Associate Director Jim Cummins after a survey trip. Learn more about this mussel.

Is It Safe to Swim?

swimmerBoating, Swimming in the Potomac River: How Safe Is It?

Judging by use, residents of the Potomac basin love their rivers and streams. As air and water temperatures rise in the summer, residents take to their favorite fishing, swimming and boating spots. Access areas and beaches along the river from its mouth to the North Branch Potomac draw crowds of people  pursuing their favorite pastimes and a love of the river resource. Learn more! 



Rain Barrels For Sale

Rain Barrels for SaleRain Bear Rain Barrels are the best design for our region. They are recycled food-grade barrels and their black colormakesthem UV-resistant so they will last outside for years. The barrels have an indented, screw-top lid that allows the water to slow and drop into the barrel. A screen in the lid prevents breeding mosquitoes and keeps debris out of thebarrel. The screen can be easily cleaned. Compression fittings on the shoulders and at the spigot mean we don't use glue or tape that can fail over time. Compression fittings are designed for underwater uses and the parts you choose to screw into them are interchangeable. Read More!

Earth Day Photo Contest Grand Prize Winner!

Patty Barker of Herndon, Va, won the top spot for "Green Drops" taken at Algonkian Park in VirginiaContest entrants sent in photos from around the Potomac watershed. The grand prize winner receives a float trip for two from River and Trail Outfitters. Special thanks to River and Trail Outfitters for their generous grand prize donation. Patty Barker of Herndon, Va., won the top spot for "Green Drops" taken at Algonkian Park in Virginia. Learn more and view the larger image...

Earth Day Photo Contest Second Place Winner!

wilson 150The second prize winner receives an REI Flashpack filled with lots of goodies, including binoculars, water bottle, and more. Special thanks to the Rockville, Md., REI for donating the second place prize. Second place goes to Kristine Wilson, Cumberland, Md., "Sunrise on the Potomac," shot near Cumberland, Md. Learn more and view the larger image...

Earth Day Photo Contest Third Place Winner!

russell 150The third place winner receives an ICPRB Rain Bear rain barrel and upper Potomac map set. Special thanks to the third place prize donor, ICPRB's rain barrel program. Third place goes to Annabel Russell, Waldorf, Md., "Wetlands on the Potomac," shot at Smallwood State Park in Md. Learn more and view the larger image...