Police are pressing for the cause of a shocking jet ski crash that left a teenage boy dead and another in hospital with a severed arm.
Emergency crews were called to Tom Uglys Bridge at Sylvania, in Sydney's south, about 6pm on Tuesday following reports of people floating in the water.
A 15-year-old was found dead in the water. Crews were able to rescue a 14-year-old and pulled him to shore.
The 14-year-old's arm was severed, and he was taken to Sydney Children's Hospital, where his condition has been upgraded to stable.
Friends and family of the 15-year-old gathered on Wednesday night near the site of the crash, where memorials were laid out.
A wooden cross at the site read "Long Live Mitch".
Superintendent Donald Faulds said the cause of the crash remained unknown.
"We believe they were on a jet ski that was owned by one of the families (but) we don't know what they've collided with," he said.
"(We) are looking at all different areas of the investigation, whether it was something to do with the bridge, something that was maybe submerged, or another item nearby."
Most debris had been removed from the water but the main body of one jet ski had yet to be recovered, Supt Faulds said.
Both teenagers were wearing life jackets at the time of the crash.
Paramedic Scott McNamara said a police officer had approached him as he suited up for the rescue and described himself as a good swimmer.
"Two (people) to effect a rescue like that makes it so much easier ... the victim was floating away from us at the time, it was probably 60 metres we had to swim to catch up to the victim," he said.
"It's an absolute tragedy and my condolences to the family of the deceased, but to have saved that young guy, that's why we do this job."
