Adam Walker was swimming the Cook Strait between the North and South Islands of New Zealand, when he looked down to see a huge shark swimming beneath him.
Just before he noticed the shark, Adam had been joined by a pod of dolphins - who are known to protect people from attacks in the ocean.
The pod spent an hour swimming alongside Adam, with the shark never attacking him on his almost 9 hour journey.
Adam is currently undertaking the Oceans 7 - swimming long distance stretches of water across the globe, including the Irish Channel, the Cook Strait, the Molokai Channel, the English Channel, the Cataline Channel, the Tsugaru Strait and the Strait of Gibraltar.
His latest ordeal was number 6 of the swims, which are all to raise money for the Whale and Dolphin Conservation Society.
On his Twitter page, Adam described the experience of swimming with dolphins as a 'dream come true.'
On a previous swim across the Molokai Channel in Hawaii, Adam was stung by a Man of War jellyfish - which left him in agony.