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 hail stones," 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.
"EMS was on scene within minutes. They set up EMS command, nine ambulances were here, and everybody was transported to the hospital, Management Coordinator Bill Oettinger said.
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.
While some have been singing the praises of the staff, others say they wished they had more direction from the pool staff about what to do and where to go for safety during the storm.