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90.5 WESA's Good Question! series is an experiment where you bring us questions—and we go out to investigate and find answers.So: What have you always wondered about Pittsburgh? Are you curious how your neighborhood originally received its name? Or maybe why the Mon and Allegheny Rivers are different colors when they merge at the Point? Or maybe you've always wanted to know what happened to all of our street cars and inclines? From serious to silly, we're here to help.

Pittsburgh boasts a trio of tributaries, but are there really three separate rivers?

Margaret Sun
90.5 WESA
The Allegheny River, as seen from downtown Pittsburgh. Clarion University Aquatic Ecologist Andrew Turner says if rivers were named by volume of their largest tributary, the Mississippi River could technically be called the Allegheny River.

Next to steel and Super Bowl championships, Pittsburgh is synonymous with three rivers. In the summer, the Three Rivers Arts Festival dominates downtown and the moniker is part of a number of companies in the region -- not to mention there used to be a stadium that bore the name.

But does the city technically have three distinct rivers?

Lorraine Caplan, of Squirrel Hill, and Ken Jakub, of McCandless, wondered, too. Both asked if the Allegheny and Monongahela rivers truly formed a new waterway with the Ohio.

Clarion University Aquatic Ecologist Andrew Turner,an expert in limnology, the study of bodies of fresh water, said technically, no, there are not three separate rivers.

“That’s just a way of breaking things up to make it easier to organize,” Turner said. “That’s an attempt to sort of put a human structure on a natural process.”

Turner said changing the name of a river is usually related to aregion’s history or the culture surrounding the waterway. The Ohio, for example, means “Great River” in Seneca and Iroquoian.

Credit Keith Srakocic / AP
Boats from the Gateway Clipper fleet float at Pittsburgh's confluence. Pittsburgh has always been known for its three rivers, but some water experts say geologically, there are two.

But if rivers were named based on limnologic factors alone, Turner said downstream waterways would more likely bear the name of their largest tributary. 

At the confluence of the Mississippiand the Ohio Rivers in Cairo, Ill., the Ohio is 281,500 cubic feet per second, while the Mississippi just upstream in Thebes, Ill. is 208,200 cu ft/s. Following the Ohio upstream to Pittsburgh, the Allegheny is about 19,750 cu ft/s, while the Monongahela is only 8,433 cu ft/s.

By that measure, the Mississippi River could actually be called the Allegheny.

Turner said he recognizes that the method can be confusing, considering it’s rare to name rivers this way, but it’s fun to think about. He said the U.S. Geological Survey, which names and documents rivers, won’t be changing the name of the Mississippi any time soon.

“They heavily weigh the traditional, cultural names of rivers in making those choices,” Turner said.

Credit U.S. Geological Survey
This map from the U.S. Geological Survey shows different regions of the hydrological unit code, another method of categorizing rivers and other waterways. Pittsburgh's rivers are in the Ohio drainage basin.

Another method used by limnologists is thehydrological unit code,or, HUC, system, in which rivers are assigned codes based on regions, watersheds and tributaries. The Upper Allegheny River’s HUC is 05010001, while the Upper Monongahela’s is 05020003.

Turner said that while the HUC system makes a lot of sense, it “hasn’t really caught on outside of scientific circles.”

Rivers could also be named by following their lengthiest tributary upstream. 

With that example, the Madison River in Yellowstone National Park, Wyo., at 183 miles, would be the headwaters of the Mississippi, and therefore warrant its namesake.

So barring any striking geological evidence, Turner said there will always be three rivers in Pittsburgh.

What have you always wondered about the Pittsburgh region? Submit to our Good Question!series and we’ll go investigate and find answers. 

Katie Blackley is a digital editor/producer for 90.5 WESA, where she writes, edits and generates both web and on-air content for features and daily broadcast. She's the producer and host of our Good Question! series and podcast. She also covers history and the LGBTQ community.