10 Remarkable Facts About the Potomac River

Written by Erin Cafferty
Updated: November 11, 2023
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The Potomac River is a historical waterway on the eastern shore of Virginia. It runs through five different states, reaches a maximum depth of 107 feet, and even has sharks swimming in its waters. There are more remarkable facts about the Potomac River to discover, so let’s go!

1. The River Starts in a West Virginia State Park

Children playing on a beach with a lifeguard watching

Point Lookout, Maryland is where the Potomac River flows into the Chesapeake Bay.

©Malachi Jacobs/Shutterstock.com

Before we get too deep, we need to start from the beginning. Where does the Potomac River start?

West Virginia’s Fairfax Stone Historical Monument State Park is where the river begins. Following its journey east, it winds its way through mountains, meets with other rivers, tumbles over waterfalls, and finally flows into the Chesapeake Bay at Point Lookout in Maryland.

2. At the Deepest Point, the River Reaches Depths of 107 Feet

Seneca Rocks Roy Gap Road looking north over the North Fork South Branch Potomac River, West Virginia.

The Potomac River averages about 24 feet deep.

©Jordan Kercheff/Shutterstock.com

At 405 miles long, the Potomac River has an average depth of 24 feet. However, the deepest point of the Potomac River is 107 feet deep! As impressive as that seems, the Hudson River — the deepest river in the U.S. — reaches a dizzying depth of 216 feet.

3. The Potomac River Is Over Two Million Years Old

Rapids in the Potomac River at Great Falls, seen from Olmsted Island at Chesapeake & Ohio Canal National Historical Park, Maryland.

Rocky terrain lines many miles of the river — it cut through the mountains to form over two million years ago.

©Jon Bilous/Shutterstock.com

Over 2 million years ago, the Potomac River as we know it formed as a result of erosion as the water cut through the mountains. Fluctuating sea levels affect the depth of the water, which is why the river has both deep and shallow areas.

4. The River Was Used by Troops and Slaves During the Civil War

Stonewall Jackson Lake

The Potomac River was used by troops and escaped slaves alike during the Civil War.

©Malachi Jacobs/Shutterstock.com

You might wonder what’s so famous about the Potomac River. During the Civil War, both U.S. troops and slaves encountered the mighty river. However, one side saw it as a challenge and the other as a corridor.

While Union and Confederate troops saw the river as an obstacle to cross on their way into battle, slaves escaping to freedom through the Underground Railroad found that the Potomac was deep enough for a small boat to cross and shallow enough to walk, ride, or drive a wagon through.

5. You Can Find Dolphins and Sharks in the Potomac River

Bull Sharks Underwater

Bull sharks can live in low-salinity environments like at the mouth of the Potomac.

©Martin Prochazkacz/Shutterstock.com

Are you surprised by the fact that there are dolphins in the Potomac River? Between July 2015 and October 2018, the Potomac-Chesapeake Dolphin Project reported over 250 mothers and almost 300 calves.

Well, sharks live there too! Sandbar, sand tiger, smooth dogfish, and bull sharks all congregate at the mouth of the river.

6. Celebrities Have Tested the River’s Waters

A woman in a swimsuit swims in a mountain river, The girl goes into cold water, Picturesque place of Turkey.

Fun fact, it is still illegal to swim in portions of the Potomac River due to its high levels of contamination.

©Photo Volcano/Shutterstock.com

Since 1971, it has been illegal to swim in the waters of Potomac between Great Falls and the southern Maryland/DC line. That’s because it’s alleged to have unsafe levels of contamination and dangerous undercurrents. However, DC residents are quick to point out that other rivers with similar cleanliness levels are legal to swim in.

Finally, in 2022, the tides began to shift. The House passed HR 7776 as a way to appease the community, which has pushed to lift the decades-long ban.

So no, you still can’t legally swim in the DC section of the Potomac River. But according to musician Lorde, you can… just don’t let the authorities catch you!

7. The Potomac River Supplies 6.11 Million People Within Its Watershed

Alexandria and the waterfront property along the Potomac River in northern Virginia

Modern waterfront property rests along the Potomac River in the historic city of Alexandria, Virginia.


Why is the Potomac River important? Well, the fact is that the Potomac River covers almost 15,000 square miles and supplies water to 6.11 million people. The health of the basin equates to the health of millions of residents, which is why restoration and conservation efforts are in place today.

8. The River Spans Across Five U.S. States

View of the Washington, D.C. skyline from the Potomac River.


The longest river in the U.S. is the Mississippi, which runs through 10 states. Meanwhile, the Potomac River spans across five — West Virginia, Virginia, Maryland, Pennsylvania, and the District of Columbia.

9. There Are Many Ways to Cross the Potomac River

Richmond Railroad Bridge Crossing the James River

This concrete arch railroad bridge spanning the James River was built by the Atlantic Coast Line, Fredericksburg, and Potomac Railroad in 1919 to route transportation of freight around Richmond, VA.

©Xavier_Ascanio/iStock via Getty Images

At 383 miles long, there are plenty of bridge crossings over the Potomac. Some of the most popular are the:

  • Harry W. Nice Memorial Bridge
  • American Legion Memorial Bridge
  • Woodrow Wilson Memorial Bridge
  • Arlington Memorial Bridge
  • Theodore Roosevelt Bridge
  • Francis Scott Key Memorial Bridge
  • Chain Bridge
  • B&O Railroad Bridge

10. The Potomac Is a Freshwater River

Great Falls National Park

The river runs through Great Falls Park in Virginia.

©Hiram Rios/Shutterstock.com

The Potomac is a freshwater river, but it converges with the brackish waters — which contain more salinity than freshwater, but not as much as salty seawater — of the Chesapeake Bay in the Potomac Estuary.

This is why you see the types of sharks that can live in low salinity conditions swimming in the Potomac!

Recap of Remarkable Facts About the Potomac River

Bet you never knew a river could be so fascinating! To conclude, let’s summarize what you just learned.

#1The river starts in a West Virginia state park
#2At the deepest point, the river reaches depths of 107 feet
#3The Potomac River is over two million years old
#4The river was used by troops and slaves during the Civil War
#5You can find dolphins and sharks in the Potomac River
#6Celebrities have tested the river’s waters
#7The Potomac River supplies 6.11 million people within its watershed
#8The river spans across five U.S. states
#9Eight bridges cross over the Potomac River
#10The Potomac is a freshwater river

The photo featured at the top of this post is © Jon Bilous/Shutterstock.com

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About the Author

Erin Cafferty is a writer at A-Z Animals where her primary focus is on horses, mountains, and parks. Erin holds a Master’s Degree from Radford University, which she earned in 2018. A resident of Virginia, Erin enjoys hiking with her dog, visiting local farmer's markets, and reading while her cat lays on her lap.

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