"Mum has then come outside and found him floating face down. She's removed him from the pool and called emergency services, then performed CPR."
Paramedics arrived soon after and were able to resuscitate the teenager. He was taken to Middlemore Hospital.
His injuries are life threatening and there are grave concerns for his health.
Mr Culpan said the incident was tragic.
"He's 16, he's not a kid so it's not a question of supervision or that he was doing anything overly silly. It's just a horrible tragedy.
"As a parent, for me this is absolutely tragic."
Victim Support has been working with the family.
Police said yesterday that the neck injury meant he could not move in the pool, and effectively he had drowned as a result.
Mr Culpan said the pool was about 182cm in diameter and less than a metre deep. It had plastic sides and was quite substantial in size - not a paddling pool.