If you spot heads bobbing in the Hauraki Gulf this morning, don't be alarmed.
Thirteen swimmers are facing the cold and swimming 20km from Matiatia Bay on Waiheke Island to Mechanics Bay in downtown Auckland.
The swimmers are raising money for the Auckland Westpac Rescue Helicopter, which flew to Waiheke Island to pick up sick and injured patients 232 times last year.
Of 1060 helicopter missions last year, that represented 22 per cent, making it the helicopter's second-most visited region.