Thames Valley Police was called at around 3.55pm to reports of an 11-year-old girl in difficulties at Liquid Leisure Windsor in Horton Road, Datchet.
Officers worked with Royal Berkshire Fire and Rescue Service, Buckinghamshire Fire and Rescue Service, Surrey Fire and Rescue Service and South Central Ambulance Service to respond immediately to the report and an extensive search was commenced, with support from the National Police Air Service (NPAS).
Following this search, a girl was located at around 5.10pm and she was taken to Wexham Park Hospital but has sadly died.
The girl’s death is being treated as unexplained and an investigation has been launched.
Although formal identification has yet to take place, the girl’s next of kin have been informed and they are being offered support by officers.
Local policing area commander for Windsor and Maidenhead, Superintendent Michael Greenwood, said: “My thoughts are with the family and friends of the girl who has died as a result of this tragic incident.
“We are in the early stages of investigating this incident to understand the full circumstances
“There was a swift response from all emergency services and following an extensive search of the lake, the girl, who was 11, was located at around 5.10pm and taken to hospital but sadly died.
“This has been an extremely traumatic and upsetting incident for all involved.
“I am aware that several members of the public entered the lake shortly after the girl got into difficultly, but were unable to locate her.
“I would like to commend them for their courage and bravery.
“My sincere condolences are with the girl’s family and friends, and I would ask that their privacy is respected at this incredibly traumatic and distressing time for them.”