People who were rescued from Hidden River Cave celebrate Thursday. Flash floodwaters started to fill the cavern during a tour, trapping 19 people. All of them were rescued.

HORSE CAVE, Ky. — Gary Russell was a mile deep in a Kentucky cave, leading a group of geology students on a five-hour tour, when he turned a corner and saw water rushing by where water wasn’t supposed to be.

He had no way to communicate with the outside world Thursday afternoon. He had no idea that a flash flood was pouring through the cave’s passages toward them, or that dozens of rescuers were already gathering at the entrance to begin a perilous hours-long journey to rescue them.

All he knew was that water wasn’t supposed to be this deep in the cave and that meant trouble.

Russell and his group were among 19 people who escaped the flooded Hidden River Cave through neck-deep water and rushing currents. It was pitch black.

“It was shooting waterfalls out of the ceiling. The walls were thundering, there was so much water moving through it,” said David Foster, the executive director of the American Cave Museum at Horse Cave and a guide for 30 years. “You just don’t know what Mother Nature is capable of. There’s only so much cave, and there’s way more water.”

The group that spent more than six hours inside the cave included Clemson University students, four tour guides and two police officers who got trapped when they tried to rescue the group.

Authorities didn’t know exactly where the missing cavers were underground, and the only light the group had came from headlamps they wore.

Heavy rains began pouring down hours after the group ventured inside, Foster said. The storm hit earlier and harder than expected, and Foster grew so worried that he decided to call authorities and trek inside to get them.