How Long is the Potomac River?

Written by Nilani Thiyagarajah
Updated: August 29, 2022
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Many people have learned about the Potomac River in American history. It’s where George Washington set up his home, giving this river the permanent standing as the “Nation’s River.” This river has also been used as a boundary between states and was part of the subject of a dispute between Maryland and Virginia about state lines.

The Potomac River has played a major role in the history of the country, in addition to offering a rich diversity in both culture and wildlife. So how long is the Potomac River, exactly? We’re going to dive right in to explore the answer to this and many other questions about this great river!

Where does the Potomac River start?

The Potomac River starts with the North Branch and South Branch, both flowing northeast until they converge.


The Potomac River actually starts as two separate branches, both flowing northeast until they converge to form the start of the river.

The North Branch starts at the Fairfax Stone (a monument erected to demarcate the start of this tributary), which is located at the junction of Preston, Tucker, and Grant Counties in West Virginia. After the Fairfax Stone, this Branch flows about 27 miles to Jennings Randolph lake, which is a man-made lake designed for emergency water supply and flood control.

After crossing the dam of the lake, the North Branch goes through the Eastern Allegheny Mountains and turns southeast around Cumberland, Maryland. It converges with the South Branch about 103 miles from where it started.

The South Branch starts close to Hightown, in Northern Highland County, Virginia. It starts on the eastern side of Lantz Mountain and flows northeast before it converges with Strait Creek and then flows north into West Virginia. The South Branch travels past multiple small mountain ranges and converges with multiple small tributaries before meeting with the North Branch.

These two branches come together about 15 miles south of Cumberland, Maryland. And this is the start of the Potomac River!

What states does the Potomac River go through?

The basin of the Potomac River includes parts of Virginia, West Virginia, Pennsylvania, and Maryland, in addition to Washington D.C. This area is referred to as the Potomac watershed. This watershed encompasses about 14,670 square miles of land area. About 60% of this watershed is forested.

Although the river meanders quite a bit, its general direction is first northeast (the two initial branches), then east, then southeast as it approaches Chesapeake Bay. In addition to the two initial branches, many tributaries flow into the river throughout its course. Some include the Anacostia River, Cacapon River, Monocacy River, Savage River, and Seneca Creek.

The Potomac River forms the boundary between Maryland and West Virginia and between Maryland and Virginia. About 10 miles north of Washington, D.C., it rapidly descends about 90 feet in a three-mile stretch known as the Great Falls of the Potomac.

Where is the mouth of the Potomac River?

The Potomac River ends when it empties into Chesapeake Bay after passing Washington D.C.


The Potomac River flows into Chesapeake Bay at Point Lookout, Maryland. Before actually reaching the mouth, the river meets the tide and becomes an estuary.

The Potomac River is one of over 150 major streams and rivers that flow into Chesapeake Bay. This area is located in the Mid-Atlantic region and is about 73 miles from the Atlantic Ocean.

How long is the Potomac River?

Great Falls Park

The Potomac River is about 405 miles long, measured from Fairfax Point to the mouth at Chesapeake Bay.

© Rissing

It can be kind of difficult to figure out the length of this particular river. It does not spontaneously start as the Potomac River at one point but as the convergence of two separate branches. Generally, when people talk about how long the river is, they measure the North Branch and the river.

Even this can be somewhat tricky since some would argue that the North Branch actually starts before Fairfax Stone. The source of the water is actually located further west than the Fairfax Stone, upstream. However, because Fairfax Stone had already been established, it was ultimately decided that this was going to be the official beginning of the North Branch.

Considering the North Branch and the main stem of the river, the Potomac River is approximately 405 miles, or 652 kilometers, long.

It also holds the title of the fourth-largest river on the Atlantic coast. This has been calculated based on the overall area of the river, including the drainage area of 14,760 square miles.

How wide is the Potomac River?

The Potomac River gets noticeably wider after it passes through Mount Vernon. Upstream, starting at Great Falls and going up to about Harpers Ferry, it is an average of about 1,300 feet wide. At the mouth, where it dumps into the Chesapeake Bay, between Point Lookout and Smith Point, the river is about 11 miles wide.

How deep is the Potomac River?

The Potomac River is 107 feet deep at its deepest point.

© Bilous

As with almost any river, the depth of the Potomac River varies from point to point. However, it’s interesting to note that the river does not get very deep until it’s downstream. On average, before this point, it’s no more than two to four feet deep.

At its deepest point, near Morgantown, Maryland, the river is 107 feet deep. In the tidal portion downstream from Washington, D.C., a channel depth of 24 feet is maintained.

What animals live in the Potomac River?

Due to ongoing conservation efforts, the 405 miles of Potomac River is as healthy as it has been in decades. Not only does this mean cleaner water, but it’s great news for several animals. The animals that have recently made a comeback to the Potomac River basin include the following:

There are many other animals who live and thrive in the Potomac River as well, including eels, river otters, and dolphins. In addition to this, there is a variety of game fish. Smallmouth bass, channel catfish, flathead catfish, muskellunge, and walleye populate the northern Potomac River.

The southern Potomac River is full of catfish (including blue and flathead catfish), sunfish, crappies, perch, longnose gar, chain pickerel, bowfin, and the northern snakehead.

The photo featured at the top of this post is © Doubletree Studio/

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