When it comes to Pittsburgh folklore, it's one of the favorites: Is there an underground fourth river? Does it provide water for the Point State Park Fountain? 90.5 WESA's Megan Harris and Margaret J. Krauss explore what's real and what may be a bit exaggerated.

Pittsburghers have long been fascinated with the mysterious, underground “fourth river.” As much as they gush about the three visible rivers, they’re often eager to tell you about the secret waterway beneath the Golden Triangle.

For our Good Question! series, we had Heather Harts, from Johnstown, ask about the rumor, but we’re sure she's not the only one curious.

There has been a lot of great reporting on this topic in the past, especially from 90.5 WESA’s very own Margaret J. Krauss. In short, Pittsburgh sits atop an aquifer. An aquifer is a layer of permeable rock, like limestone or sandstone, through which tiny threads of water can easily move.

Margaret explains how the Century Building along 7th Avenue downtown is heated and cooled by the underground aquifer.

The Pittsburgh City Paper’s Chris Potter noted in 2013 that other Downtown buildings, such as PPG Place, also use the underground aquifer for heating and cooling -- a more useful application than extracting water, since, as Potter pointed out, it's 30 feet below ground.

Pennsylvania is also home to 80 trillions of groundwater, 9 million of which was extracted using downtown wells in 1950, as Krauss offers more context in an October 2015 Pittsburgh Magazine article.

So why did we take to calling it a river? Well, it’s not really easy to visualize groundwater. Most people imagine it collecting in a body or moving in a channel. While there may be a river’s worth of water underneath Pittsburgh, it’s distributed through tiny gaps between or within rock layers, millimeters thick. True underground rivers are found only in cavernous rock formations where the rock has been dissolved.

When the North Side T connector was being constructed, the Pittsburgh Post-Gazette’s Mark Roth laid to rest fears that the underground aquifer would be affected by tunneling.

White it’s true that the fountain at the Point draws its water from the aquifer, there’s no river or channel of water to behold underneath. Nor does the water shoot from below like a natural geyser. Instead, the water is pumped from an underground bed of saturated sandy rock.

For this, we have tens of thousands of years of glacial displacement -- the Wisconsin Glacial Flow -- to thank. A Pennsylvania Department of Conservation and Natural Resources geology magazine explains the city’s river development over the past 1 million years.

It’s not clear how and when the rumor about the fourth river started. In a 1991 article for the Deseret News in Utah, Jan Harold Brunvand recalls receiving a postcard from a University of Pittsburgh professor, which on the back read:

"The Great Fountain of Point State park has become a focal point and landmark of Pittsburgh's Golden Triangle. Largest in the U.S., this dramatic tower of water soars 200 feet at the confluence of the Monongahela and the Allegheny Rivers forming the Ohio. The Fountain's origin lies not in these three rivers but in a little-known fourth river underground."

The Deseret News article, as well as one by “Professor Buzzkill” of Steel This Magazine, include mentions of fourth-river associated Pittsburgh folklore: the whereabouts of the B-52 bomber and the Green Man. Both are interesting stories that we’ll share for another Good Question!

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

Update 5/2/17 1:50 p.m.: This article has been corrected to reflect the spelling of Deseret News.