By LUKE SALKELD

Last updated at 10:33 03 April 2008

Gliding through the ocean in temperatures below freezing, she swims effortlessly through the water with nothing to help her breathe.

And the Beluga Whale seems to be managing pretty well too.

This is the extraordinary moment when the graceful mammal bumped into a free diver swimming in Russia's White Sea.

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Whale rider: Free diver Julia Petrik hitches a ride with a passing Beluga whale

Julia Petrik, had to cut through ice one foot thick to get in to the -2C (28F) water off the north-west coast of the country.

Miss Petrik, 38, one of the world's top free divers, swims underwater with no air tanks and can hold her breath for up to two minutes.

After entering the water she grabbed hold of a passing Beluga Whale for a lift - a moment captured by British photographer Dan Burton.

Writing on her website, Miss Petrik says she needs to stay in top physical form to perform her extreme dives.

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Brief encounter: Julia Petrik spent just a few seconds with the Beluga whale

Going up?: Julia Petrik clings to the whale as it ascends

She says: "Diving to such a depth and holding your breath by only using the power of your body is impossible without good physical form, muscles and endurance.

"It is a case of straining but not straining at the same time.

"But it is not just the power of your body - it is managing the control over consciousness, ideas, emotions and sensations to push yourself to the limit.

"The relaxation that is created under the water is boundless. It is a demanding sport as well as a full time job."

Miss Petrik is an instructor for the International Federation of Free Diving and is Russia's champion free diver.

Mr Burton, 41, from Topsham, Devon, dived below her in scuba gear to photograph his subjects using specialist underwater camera equipment.

He said: "The way Julia moves through the water is just incredible.

"You have to be careful of hypothermia when you are in there.

"I was worried I was going to freeze but in the end I was in the water for an hour and could easily have stayed longer."

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Back on dry land: Julia Petrik with her special free diving flippers

Temperatures above the ice were as low as -15C (5F) and during the free-dive Miss Petrik swam to depths of 82ft, wearing only ultra-tight wetsuits, face masks and flippers.

Miss Petrik managed to grab the whale for a free ride at around 26ft and floated for several seconds before letting go.

Beluga Whales only live in Arctic and sub-Arctic waters and are protected from the sub-zero temperatures by a thick layer of blubber.

The elusive whales are an unmistakable all white in colour with a distinctive melon-shaped head and can grow up to 16ftin length.

Scientists say Belugas have been known to live up to 50 years in the wild and have been recorded diving to depths of over 2,000ft.

Mr Burton added: "It was an unbelievable experience to be with these animals. One of them even grabbed hold of my arm and my leg with its mouth.

"What was amazing was how dark it was underneath the ice. When you looked up there was this green glow - it was like another world, breathtaking."