But the men and women in snorkels and masks were elite athletes, diving for time bonuses to put their team ahead on day four of the 350-kilometre Mark Webber Tasmania Challenge.

The multi-sport competitors resembled an adventure tourism group as they beached their kayaks and dived off the rocks of Binalong Bay in search of metal strips.

It was a unique twist on a day when athletes ran, paddled and biked through 70 kilometres of the Bay of Fires and into Georges Bay at St Helens.

Blustery conditions failed to mask the breathtaking scenery of lichen-coated granite, azure waters and white sands, with coastal landmarks Cosy Corner, Swimcart Beach and Sloop Rock part of the course.

The Binalong Bay residents that gathered to watch the snorkel leg were impressed by the star power of the event: athletes present including ironmen Shannon and Caine Eckstein and Darren Mercer, rising pro surfer Sally Fitzgibbons, and former AFL stars Glenn Archer and Leigh Colbert.

Shack owner Val Carey was "quite chuffed" to be standing less than two metres from event founder and formula one competitor Mark Webber.

"He's a lot skinnier than I thought he'd be," Mrs Carey said.

"But it is fantastic to see him and all these other high-profile people.

"It's a great thing for the area to have this event come through."Today is the fifth and final day of the 2012 Mark Webber Tasmania Challenge, with racers to complete a 50-kilometre course around Hobart.