Auckland's Olympic Pools facility is reviewing its rules around breath-holding training after two men were rushed to hospital in a critical condition.
It's believed the two young men taken to Auckland Hospital on Saturday night were deliberately holding their breath underwater at the Newmarket facility.
Water safety experts say doing breath-hold exercises without a buddy or spotter is highly risky, and the two men were lucky another swimmer spotted them before it was too late.
Competitive swimmer Joel Crampton was in the water training when he noticed the two men underwater in the deep end.
He told Newshub they appeared to be holding their breath.
"It looked like they knew what they were doing so I let them be for a little bit and did a few lengths," Crampton said.
He said after his laps, the pair "were still down there not moving" and the lifeguard started getting concerned.
"I swam down to see if they were responsive and they weren't so I pulled them both up."
Emergency services arrived quickly and helped pool staff and a doctor who happened to be swimming to revive the men.
"It wasn't nice pulling a limp body up from the bottom of the pool but I'm glad I was there and able to do it, and I hope it's made a bit of a difference for them," Crampton said.
They were taken to Auckland Hospital in a critical condition.
Olympic Pools and Fitness Centre director Peter Rust told Newshub his staff acted quickly and followed emergency procedures.
"I have to say they did a fantastic job, everything kicked in in terms of their professional training, they responded very well and had very good assistance from other people," he said.
It's believed the two men were deliberately holding their breath - which is a practice the pool discourages.
"We have no problem with freediving and training for it, but in a controlled situation. In the weekend or in the evening, it's not appropriate."
There are certain breath-hold techniques that present a risk of 'shallow water blackout'.
Auckland University anaesthesiology lecturer Jonathon Webber told Newshub "the normal precursor to these events is people hyperventilate".
"When they do that, they interfere with the body's intrinsic safety measures that remind you to take a breath and often what happens in these situations is the person is unaware that their blood oxygen levels are getting critically low and they faint."
Webber said it's highly unusual for this to happen to two people at the same time, and they were very lucky they were noticed.
"It's not within the lifeguards' abilities to observe what's going on underwater, so unless someone's swimming past with goggles to see it, then it's a very risky activity," he added.
In a statement, the family of one of the boys said their son was swimming to touch the bottom of the pool, which is 5 metres deep, and did not surface.
"Our son was not practicing freediving and he was not deliberately holding his breath underwater," they said.
"We would like to thank the retired doctor and competitive swimmer, Joel Crampton who assisted our son and first responders including Hato St John and the NZ Police.
"This is a tragic accident that occurred while swimming and we request that you respect our privacy at this time."
This story has been updated to include the family's statement.
