Jo Davidson (C) and her fellow members of the Coogee Cougars running group prepare to enter the water for the "Sydney Skinny" - in what is dubbed the first mass nude ocean swim. (AFP PHOTO/William WEST)

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Ahead of her first nude ocean swimming race, 43-year-old Sydney mother Jo Davison was a little nervous.

She had every reason to be. Australian ocean swimmers have plenty to worry about, from avoiding stinging bluebottle jellyfish and the flailing limbs of other swimmers to the sharks known to inhabit Sydney Harbour.

And of course, the issue of achieving all of that while wearing nothing.

"This is very confronting for all of us," Davison said ahead of plunging into the calm waters of Cobblers' Beach, one of more than 650 people who stripped naked to take part in last month's inaugural Sydney Skinny.

But like many who anxiously took to the lapping waves, she emerged shortly afterwards having completed the 900 metre dash with her Coogee Cougars, a group of women who regularly run together for fitness, saying she felt great.

"It feels quite liberating," she said, as she wrapped herself in a sarong.

"This is something we would never normally do... It's something that is outside your comfort zone. So, before, we felt very nervous, very anxious. And now that we have done it, we all feel great. It's a one-off."

Davison said for her group of women it was a celebration of their bodies.

"Fortunately we have here together a group of women whose bodies do us very proud -- we've had children, we run together, we train together, we're fit, we're healthy and I think it's time we gave our body thanks for the good bits, the indifferent bits," she said.

"But above all it's a celebration of us all together."

This is just the spirit that event organizer Nigel Marsh had in mind when he had the idea to launch a nude swim which also raised money for the National Park in which is it set.

The event is not for naturists, and it's not a spectator sport, he insists.

"It's a joyous community celebration where you are pushed slightly outside your comfort zone and you're made to feel better about yourself and the world around you," he told AFP.

"It's all ticketed, there are no spectators, no-one is going to see you.

"The worse that can happen is that one person sees your bare arse for one second. And if you think the world is going to stop spinning because that happens, you need to get a reality check.

"This is about acceptance, and all the good things in life and spreading the joy."

Marsh, who claims he never skinny dips, says he wants to make the world a better place "one swim at a time" and hopes the Sydney event becomes an annual one that celebrates the spectacular beauty of the city.

The event has a 'feel-good' vibe, with a guitarist making music for those disrobing and plunging into the water, some wearing flippers and one woman wearing nothing but a fake flower garland around her waist.

"It feels like a party," said Dunstan Bertschinger.

For more experienced ocean swimmers, such as Duncan Adams who in 2010 swam the English Channel, the Sydney Skinny is just the latest example of the explosion of ocean swimming in Australia.

"When I first started ocean swimming in 2002, there would have been 10 or 11 events across New South Wales, there 20 or 30 every week now," he said after finishing the nude swim.

At Cobblers' Beach, swimmers emerging from the water and gratefully taking the sarongs offered by volunteers at the water's edge, praised the event.

"You just feel free and it was lovely," said Jeanette Adams.

"And there are so many people doing it with you... It was great. Everybody just loses their inhibitions. Lot's of fun."

"I felt free, I felt exhilarated, it's beautiful," agreed fellow participant Rod Stanley-Jones.

"Everyone should do it. It's only once a year so come on down next year!"