A teenager had his life support turned off on Tuesday after he was found floating in the bottom of a swimming pool last week.
Nelson Bays area commander Brian McGurk said Sam Goodenough, 16, of Richmond, was pulled unconscious out of a pool at 12.50pm on December 29.
"The kids thought he was playing around," Mr McGurk.
Ambulance officers revived the teenager and took him to Nelson Hospital, where he was admitted to the Intensive Care Unit.
Sam's life support was turned off on Tuesday.
Mr McGurk said a post-mortem indicated he had drowned.
He said there had been reports Sam had been competing with friends to see who could hold their breath the longest.
The death has been referred to the coroner.
Sam's father, Geoff, told the Nelson Mail it was a tragic drowning and Sam and his friends had been having a competition to see how long they could hold their breath underwater.