Lower Southampton Township workers surveyed the damage at Dolphin Swim Club, a public swim club run by the township, one day after a quick-moving storm blew through.
The pavilion-like tent was left mangled, crushed by a tree that authorities say was struck by lightning.
"Witnesses in there told me there were lightning strikes immediately before the tree was damaged and there was quarter-sized hailstones," said Lower Southampton Township Supervisor Raymond Weldie.
Township officials say nine people inside the tent were injured - three seriously.
Two adults and seven children were taken to hospitals, according to authorities.
"One big tree fell down right where the little kids playground is at," said pool-goer Alex Serrano.
Management Coordinator Bill Oettinger said, "EMS was on scene within minutes. They set up EMS command, nine ambulances were here, and everybody was transported to the hospital."
Pool staff say it's unknown when the club will reopen.
Officials say lifeguards and other pool staff got everyone out of the tent by the time EMS arrived.
Fred Fishman of Holland, Pa. was there at the club and says when thunder rolled in, the pool itself was evacuated. He says when the torrential downpours began, he and others sought shelter in one of the concrete buildings on site.
"It was serious heavy rain. Four-star, heavy rain. And even inside, we were getting pieces of ice the size of quarters," said Fishman.
Action News reached out to township officials on Monday for an update on the injured or to find out when the pool will reopen. So far they have not responded.