For years, the Gilded Age’s most powerful industrialists gathered at Lake Conemaugh, an idyllic body of water made possible by Pennsylvania’s South Fork Dam. Their secret retreat was a place to fish, hunt and consolidate their power.

Until May 31, 1889, that is. That’s when a dam altered by the exclusive club burst, and the unthinkable happened. Torrents of water rushed downstream as the dam failed, inundating nearby Johnstown with 16 million tons of water and wiping out much of the town. The flood ended up being the deadliest in American history. But could it have been prevented?

Disaster was far from the minds of Pennsylvania magnates like Andrew Carnegie, Andrew Mellon, and Henry Clay Frick when they joined the secretive South Fork Fishing and Hunting Club. Founded in 1879, the club was designed to give the most powerful men in Pennsylvania a quiet retreat—a place to enjoy the magnificent wealth they had accumulated in the steel, railroad, and other industries.

The club owned a private, artificial lake where they gathered in a clubhouse and private cottages to mingle and enjoy the pleasures of nature. They picnicked, swam and fished, puffing on cigars and taking advantage of a rare chance to relax.

But the lake where so much wealth and power gathered was built on a shaky foundation. Before the club bought it, the unnamed reservoir was part of Pennsylvania’s canal system. Once it came into the hands of the South Fork Fishing and Hunting Club, they modified it to their recreational interests. They added a fish screen onto the spillway—the structure built to keep water from building up too high and straining the dam. And most importantly of all, they lowered the dam, which sat right above Johnstown.

When an unusually strong storm hit the area on May 28, 1889, pounding the area with between six and 10 inches of water in just 24 hours, water levels at the dam began to rise. On May 31, Elias Unger, who managed the club, looked outside and began to worry about the rising waters He supervised a group of Italian laborers as they frantically dug a new spillway and tried to unclog the existing one.

They were too late. As the dam burst, a 30- to-40-foot-high wave rushed the 14 miles toward Johnstown. The flood was as wide as the Mississippi River and three times more powerful than Niagara Falls. As it hit Johnstown, all hell broke loose. Locomotives weighing 170,000 pounds were wrenched from railroad tracks and swept thousands of feet. Debris piled up 40 feet high; some caught fire as it hit bridges and buildings. People were sucked from buildings and tossed into a raging torrent.

“It was like the Day of Judgment I have since seen pictured in books,” Gertrude Quinn Slattery later recalled. “Pandemonium had broken loose, screams, cries and people were running.” Pets and people struggled to escape the rushing waters, but when the wall of water arrived, they were helpless. It was “a moving mass black with houses, trees, boulders, logs, and rafters coming down like an avalanche,” she wrote.

When the waters finally receded, the extent of the damage became clear. According to the Johnstown Area Heritage Association, 2,209 people died, almost 400 of them children. Among the dead were 99 entire families. The $17 million in damage (more than $4.4 billion in current dollars) included 1,600 obliterated homes and four square miles of complete destruction. In the aftermath, bodies were found as far away as Cincinnati, Ohio—more than 400 miles away.

The world rushed to help. The American Red Cross, led by Clara Barton, worked tirelessly to help injured and homeless residents in its first major initiative, and workers like morticians and builders came from all over the country. Money poured in, too.

It was the deadliest non-hurricane flood in American history, and people wanted answers. However, the powerful industrialists whose modifications had caused the flood were never held legally accountable.

In court, they claimed that they only lowered the dam by one foot and that the flood was an “act of God.” Individuals who sued all lost in court, and some even went bankrupt. Though the American legal system soon adopted precedents that made it possible to hold defendants liable for their modifications to land, the magnates behind the Johnstown Flood walked off scot-free. Nobody, it seemed, was willing to challenge America’s most powerful men.

That’s changed in modern years as scientists and historians work to reconstruct what happened during the fateful flood. Only in 2013 did researchers from the University of Pittsburgh at Johnstown find out the real truth about the club’s claims with the help of hydrological research and advanced mapping. They determined that contrary to the club’s claims, the dam had been lowered by three feet, not one, and that the changes reduced the dam’s ability to discharge stormwater by half.

It turns out that the flood could actually have been prevented—if only the magnates of the South Fork Fishing and Hunting Club had been willing to trade in a bit of their leisure for the safety of the town below.