Which US rivers also serve as borders between states?

Rivers as Borders: Where Water Draws the Line in the U.S.

Think about the map of the United States for a second. Ever notice how many state lines seem to wiggle and wander along a river? It’s no accident! Rivers have been shaping our country’s boundaries since way back when, from colonial days right up to the state lines we know and (sometimes) love today. But using rivers as borders? Turns out, it’s not always smooth sailing.

River Borders: More Common Than You Think

You might be surprised to learn just how many states rely on rivers to mark their edges. Seriously, only a handful of mainland states – I’m talking about you, Colorado, Montana, Utah, and Wyoming – don’t have a single river defining where they begin and another state ends. It’s especially common in the Midwest, the Northeast, and down South. And get this: states like Vermont, Iowa, Texas, Minnesota, and Illinois are practically surrounded by rivers!

The Big Players: Rivers That Define States

Okay, so which rivers are the biggest border-makers? Here are a few of the headliners:

• The Mighty Mississippi: Of course, we have to start with the Mississippi. This iconic river acts as a watery border for parts of ten states! Can you name them all? (Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana). That’s a whole lot of states relying on Old Man River.
• The Missouri: Longest River, Longest Borders: The Missouri River, not to be outdone, is the longest in the U.S. and carves out borders for South Dakota, Nebraska, Iowa, Missouri, and Kansas.
• The Ohio: A Boundary Back East: Head further east, and you’ll find the Ohio River doing its part, separating Illinois, Indiana, Ohio, Kentucky, and West Virginia.
• The Colorado: Out West: The Colorado River, a lifeline in the arid West, marks bits of the borders between Arizona, Nevada, and California.
• The Columbia: Northwest Divider: Up in the Pacific Northwest, the Columbia River draws the line between Washington and Oregon.
• The Rio Grande: The Rio Grande is a major border definer between Texas and Mexico, after flowing through Colorado and New Mexico.
• The Connecticut River: Separates New Hampshire and Vermont.

And that’s not all, folks! Plenty of other rivers play a smaller, but still important, role in defining state lines. Think of the Big Sandy River (Kentucky, West Virginia), the Red River of the South (Texas, Oklahoma, Arkansas), the Delaware River (New York, Pennsylvania, New Jersey, Delaware) and the Snake River (Idaho, Washington, Oregon).

The “Thread of the Channel” and Other Quirks

So, how do you actually draw a border down the middle of a river? Well, usually, it’s done by following the “thread of the channel,” also known as the thalweg. Basically, you find the middle of the river’s main channel, the deepest part where the water flows fastest, and that’s your line. Sounds simple enough, right? But there are always exceptions! In a few cases, the border is actually defined by one of the riverbanks.

Take New Hampshire and Vermont, for example. Their border is the western bank of the Connecticut River. That means New Hampshire owns the whole river along that stretch! Kentucky is another interesting case. Its borders with Ohio, Indiana, and Illinois are based on the northern bank of the Ohio River, giving Kentucky ownership of the river itself. Maryland gets the Potomac River, as the border with Virginia lies along the southern bank.

Why these weird exceptions? Well, it often comes down to old agreements, historical quirks, and even Supreme Court rulings. For example, the Kentucky border goes back to when Britain won the French and Indian War in 1763. The Supreme Court even had to step in to settle a dispute between Ohio and Kentucky, ruling that the Ohio River boundary was the low-water mark on the Ohio River’s north shore as it existed way back in 1792!

When Rivers Move: Challenges and Oddities

Using rivers as borders can get tricky because, well, rivers move. Erosion, floods, even earthquakes can change a river’s course over time. And that can lead to some seriously strange situations.

I remember reading about those earthquakes in 1811-12 that actually changed the Mississippi River’s course. Afterward, two Tennessee towns ended up west of the river, practically stranded in Arkansas! And then there’s the Kentucky Bend, a little chunk of land completely surrounded by Missouri and Tennessee because the river decided to take a detour. Talk about a geographical head-scratcher!

The Bottom Line

Rivers are a surprisingly important part of the map of the United States. They define state borders, shape our political landscape, and sometimes create a few geographical oddities along the way. So, the next time you’re looking at a map, take a closer look at those squiggly lines. You might just be surprised at the stories they tell.