Sacramento Fire Department was called to the gym located at 7th and K streets at about 12:30 a.m. Friday after a woman was found unresponsive at the bottom of a swimming pool.
The woman was swimming alone, rescue officials said.
She was discovered in the pool by a gym staffer, authorities said. Bystanders started CPR on the woman.
Firefighters said it was unclear how long the woman had been under water.
The gym remained open on Friday.