Potomac River

The **Potomac River** is located within the Mid-Atlantic region of the United States and flows from the Potomac Highlands into the Chesapeake Bay. The river (main stem and North Branch) is approximately 405 miles long, with a drainage area of about 14,700 square miles. In terms of area, this makes the Potomac River the fourth largest river along the Atlantic coast of the United States and the 21st largest in the United States. Over 5 million people live within the Potomac watershed.

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 majority of the lower Potomac River is part of Maryland. Exceptions include a small tidal portion within the District of Columbia, and the border with Virginia being delineated from "point to point" (thus various bays and shoreline indentations lie in Virginia). 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 405 miles from Fairfax Stone Historical Monument State Park in West Virginia on the Allegheny Plateau to Point Lookout, Maryland, and drains 14,679 square miles. The length of the river from the junction of its North and South Branches to Point Lookout is 302 miles.

The river has two sources. The source of the North Branch is at the Fairfax Stone located at the junction of Grant, Tucker, and 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 at Little Falls, 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 (3 traditional miles) wide at its mouth, between Point Lookout, Maryland, and Smith Point, Virginia, before flowing into the Chesapeake Bay.

## Bridges

All of the bridges along the main branch of the Potomac River south of Harpers Ferry, Virginia are significant in some way, if for no other reason than the fact that the historic remains of the Chesapeake & Ohio (C&O) Canal parallel the river along its north bank. The Point of Rocks Bridge is a multi-span truss bridge and is the only bridge along the Potomac River and its branches of said type. The American Legion Memorial Bridge carries the western loop of the I-495 Capital Beltway, and the Chain Bridge is a privately-owned toll bridge built on the site of an original wooden structure dating back to the Civil War. The Francis Scott Key, Theodore Roosevelt, and Arlington Memorial Bridges are all significant for their architecture, as is the Fourteenth Street Bridge complex, where three highway bridges and two railroad bridges all share one complex system of approaches. The largest bridge along the Potomac River, the Woodrow Wilson Memorial Bridge, carries the southeastern loop of the I-495 Captial Beltway and also Interstate 95. The Governor Harry W. Nice Bridge crosses the river near its mouth, where the river is some 3 miles wide.