10-year-old girl died at Putney Leisure Centre on Tuesday afternoon in what police are treating as an “unexplained” death.
Officers were called to the leisure centre on Dryburgh Road in south-west London at 2.46pm on Tuesday.
The girl was reported to be in cardiac arrest.
Officers and London Ambulance Service attended and administered emergency first aid.
The child was taken to hospital where she sadly died a short while later.
Her next of kin are being informed, the Metropolitan Police said.
A forensic scene is in place and enquiries continue.
Putney Leisure Centre and Wandsworth Council have been contacted for a comment.