Montgomery County Fire and Rescue took a girl from Rockville Swim Center to a hospital with life-threatening injuries Tuesday afternoon.
Units arrived quickly about 2:40 p.m. Tuesday, Batallion Chief Dee Howard said.
The girl, believed to be 10-12 years old, jumped off the lower diving board into the pool and appeared to have some kind of medical emergency, but she did not go under warning, News4's Shomari Stone reported.
Lifeguards immediately went to her aid.
A woman who was with the girl at the pool accompanied her to the hospital.
Rockville City Police are investigating.