Serene and picturesque, South Jersey quarries lure swimmers to calm waters that authorities say are deceptively dangerous.

Tethered to a rope, Devon Hausmann of the Hamilton Township Dive Team waded into the Pine Barrens quarry, often called The Blue Hole, in Winslow Township earlier this month — where no swimming signs are posted.

“It’s very warm, shallow and then out of nowhere…You just fall,” he said. “And the water temperature drops at least, 15, 20 degrees.”

Hausmann wore an underwater camera as another team member flew his drone over the water, to show why these old mines have claimed so many lives over the years.

Just last week, two 17-year-olds drowned in separate incidents in quarries in Gloucester and Ocean counties.

“You can have drop-offs to 40 feet, 60 feet,” Hausmann said.

Glenn Hausmann, another dive team member, said the sand around the holes can very easily collapse under a person’s weight. Unlike lakes, the quarry and others like it often do not become deeper gradually, but instead are riddled with cliffs that can kill.

There’s another danger. Many of these quarries are in remote areas with rugged terrain, inaccessible to emergency vehicles. So rescuers often have to walk long distances, carrying heavy equipment, just to get to the water.

“You’re 20, 30 minutes into a rescue easy…and nobody is going to be under water that long and survive,” Glenn Hausmann said.