Kiwi freedive world champion William Trubridge is attempting to swim the Cook Strait underwater to raise awareness for the endangered Hector's and Maui dolphins.
Trubridge, who returned to New Zealand shores earlier this month as his partner prepares to give birth to their first child, started the 22km swim today off the coast of south Wellington.
Coming up for air every 25 meters to take a 10-second breath, the swim will likely take Trubridge 10 hours to complete.
His father, David Trubridge, told Stuff they had done a successful trial run earlier and that this was just one of many projects Trubridge had worked on to draw attention to the Hector's Dolphin.
"It's been caught in fishing nets, its range has been hit by commercial fishing. There's only about 30 of them left," said David.