The 13-year-old was pulled from the water at Maitland Aquatic Centre just after 3.30pm.
Lifeguards performed CPR beside the pool until paramedics arrived and took over.
A teenage girl was pulled unconscious from the pool at the Maitland Aquatic Centre this afternoon.(9News)
The girl was rushed to John Hunter Hospital in a critical condition but could not be revived.
The whole incident unfolded in front of a large group of relatives and one woman collapsed from shock. It s just a very sad situation for all the people in the pool and particularly the family, Chief Inspector Tony Townsend said.