Adam Walker from Nottingham was swimming in the Cook Strait in New Zealand. During the 16-mile swim across the water body, he spotted a Great White close by.
Mr Walker said that the shark was a few feet below him while taking on the Cook Strait.
Speaking on his Youtube channel, he said: “I happened to look down and saw a shark a few metres underneath me.
“I tried not to panic as I have an objective to successfully swim across.”
Speaking to the Marlborough Express, Mr Walker shared he had a chance encounter with a pod of dolphins as the shark swam below.
He claimed the dolphins formed a protective ring around him when the shark approached, shielding him from any potential attacks.
Mr Walker added: “I’d like to think they were protecting me and guiding me home.
“This swim will stay with me forever.”
It comes as a shark attacked a swimmer off the British coast for the first time 175 years.
A snorkeler was rescued by coast guards after being bitten by a shark in Cornwall, which would mark the first serious shark attack since 1847.
A spokesman for the Maritime and Coastguard Agency said: “HM Coastguard sent Penzance Coastguard Rescue Team to meet a snorkeler who suffered a suspected shark bite.
“The coastguard was notified just before 12.30pm on Thursday, July 28. It is believed the swimmer suffered a leg injury.
“The coastguard team met the casualty at Penzance harbour to assist with passing them into the care of the ambulance service.”