There's a river in Pennsylvania whose endpoint is unknown — and it's not the only "lost" river

Researchers have sent labeled objects floating down the lost river. None have ever been seen again

By Matthew Rozsa

Staff Writer

Published April 22, 2023 1:59PM (EDT)

Lost River Caverns in Hellertown, Pennsylvania (Wiki Commons/Horseluv10)
Lost River Caverns in Hellertown, Pennsylvania (Wiki Commons/Horseluv10)

On maps, rivers are typically depicted as blue lines — with a starting point, usually near a mountain where rainwater collects; and an endpoint, usually in a lake or ocean. With the advent of satellite imagery, tracing the path of a river is typically a simple exercise; no more hacking through brush and scaling mountains to map geography.

Yet peculiarly, there are still rivers in the world, in 2023, that have unknown destinations. One such river is in Pennsylvania's Lehigh Valley. Lest you think this river is in the middle of nowhere, know that the Lehigh Valley is a mere 115 miles west of the New York City metro area, one of the most populous regions in the country.

The geological formations are meticulously formed and vividly colored, as if carved by the hand of a Renaissance artist and painted by a '90s Nickelodeon set designer.

The Lehigh Valley itself is a lush and green region of Pennsylvania (as well as my home for a quarter-century). It is located on famously fertile land, a region of tiny creeks and tributaries as well as the famous Delaware River to the east. Indeed, Lehigh Valley real estate is so valuable that the entire region was stolen from the native Lenape in 1737 with a forged document and a rigged footrace (look up the "Walking Purchase"). Cornered into the state's eastern armpit by the Blue and South Mountains, the Lehigh Valley is named after the titular Lehigh River, which roars through and powers the metropolitan area of more than 860,000 residents.

Yet there is another famous river in this region, one that has attracted thousands of tourists over the centuries. All you have to do is journey 170 feet below the surface through a series of limestone caverns filled with stalactites and stalagmites. The geological formations are meticulously formed and vividly colored, as if carved by the hand of a Renaissance artist and painted by a '90s Nickelodeon set designer. Then you arrive at the river itself: On the smaller side, but undeniably a full-fledged river, colored like the Lehigh as its gentle current echoes through the cavern's cool walls.

A "lost river," by definition, is any large and natural stream of water which flows into an underground (and often undetectable) passageway. Such is the case with Pennsylvania's aptly named lost river.

Robert Gilman — whose family has owned Lost River Caverns for generations — spoke to Salon about a particularly famous effort to understand exactly where this enigmatic river is going.

"They put information on the ping pong balls and let them float down into the stream so other people would find them," Gilman recalled. "They were never found."

"This area that we're standing in, it was a limestone mining operation that we were digging back along the whole hillside," Gilman told Salon. He explained how the cavern where we were conducting the interview had once been an active limestone quarry until quarry workers discovered the lost river and spacious caverns in 1883. By the end of the century, the caverns were a major tourist attraction in the region. One particularly spacious and brightly hued room, the Crystal Chapel, was frequently the location of major social events. Even today the Lost River Caverns are one of the defining natural landmarks of the Lehigh Valley, and many long-term residents have a personal connection to it. (In my case, a friend of mine from high school, Adam Hollingsworth, gives enthusiastic tours there.) Yet the mystery of the lost river's destination remained, thwarting human ingenuity at every turn.The most famous attempt to find its origin occurred in 1930, Gilman recalled. That was when scientists sent ping pong balls with red dye downstream "to find the destination of the river."

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"Ping pong balls would flow downstream, obviously, so they put information on the ping pong balls and let them float down into the stream so other people would find them," Gilman recalled. "To the best of my knowledge, they were never found. There may be a chamber somewhere filled with ping pong balls."

The Lehigh Valley isn't the only "lost" river, now or historically. The Roman emperor Nero was fascinated by the Nile River, which despite being the longest river in the world had an unknown origin until relatively recently. Determined to crack this mystery — especially since their hold over the Nile River was key to the Roman empire's control over northern Africa — Nero organized expeditions down the river in 60-61 AD. Eventually they got stuck in the Sudd, a giant swampy region in South Sudan. It would take centuries until explorers finally ascertained its destination as Lake Victoria, more than 6,600 miles to the south of where the Nile empties into the Mediterranean Sea.

Up at the northern end of the ancient Roman Empire, one might find dozens of subterraneans rivers flowing out of the Thames as direct and indirect tributaries. Today most of these have been covered up. That may be for the best, as for centuries they were used by the medieval English for sewage disposal. In the United States, there are famous lost rivers from Idaho to Indiana. The one in Idaho is known as the Big Lost River because, per its name, its surface flow ultimately pushes into the Earth itself, disappearing into the Snake River Aquifer near the Idaho community of Arco. Meanwhile, the most well-known lost river in Indiana rises in Vernon Township, Washington County but is mostly underground. Because there are so many underground caverns and sinkholes in the area, it has never been fully explored, and as such the lost river there could have dozens of offshoots covering hundreds of miles.

Of course, one does not have to go to well-known lost rivers to find them. Gilman himself shared one of his own favorite experiences when it comes to lost rivers other than his own.

"I also saw another one out in Wyoming that was part of the Wind River Range," Gilman recalled excitedly. "You could actually see this water flow along and would disappear into the ground. And then, I think it was maybe a hundred yard or so be downstream, it did come back up at the surface."

By Matthew Rozsa

Matthew Rozsa is a staff writer at Salon. He received a Master's Degree in History from Rutgers-Newark in 2012 and was awarded a science journalism fellowship from the Metcalf Institute in 2022.

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Furthering Geology Hydrology Lost River Cavern Lost Rivers Nero Nile Pennsylvania Rivers