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The Potomac River /pÉËtoÊmÉk/ is located along the mid-Atlantic coast of the United States and flows into the Chesapeake Bay. The river (main stem and North Branch) is approximately 405 miles (652 km) long, with a drainage area of about 14,700 square miles (38,000 kmÂ²).n 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 Great Falls of the Potomac is 3 miles downstream from here, to the southeast. Little Falls is 11 miles downstream and the estuary, at sea level, begins 13 miles downstream. The distance to the mouth of the Potomac is 130 miles.The river's overall length, from source to mouth, is 382 miles. Its average width from Harpers Ferry to Washington is 1,500 feet, except at Great Falls where it narrows to a 200-foot gorge.uman habitation in the Potomac River Basin has existed for 9,000 years, according to archeological evidence. The name Potomac derives from the Algonquian word patawomeke, which means trading place.. The first English settlement, St. Mary's City, was founded in 1634.