A teenage boy has been charged over a horror jet ski crash that claimed the life of his friend in a Sydney river.

The deceased, 15, was found dead in the water when emergency crews arrived at the Georges River, Sylvania, in July.

His friend, then 14, was rescued, but his arm was severed in the accident.

Following extensive inquiries, police issued the boy – now aged 15 – with a Court Attendance Notice for one count of dangerous navigation occasioning death, and another of operate recreational vessel negligently causing death.

He will appear before a children’s court on July 22.

At the time of the incident, police said they did not know what the jet ski had collided with.

“[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,” they said.

Both teenagers were wearing life jackets at the time of the crash, police said.

Paramedic Scott McNamara and a police officer swam into the river to try and save the accused teen as he slipped in and out of consciousness.

“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,” McNamara 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.”

The deceased’s friend Alana told The Daily Telegraph that he “had such a pure heart”.

“He always decided to help people out, even if he wasn’t good mates with them,” she said.