A kitesurfer who crashed his hyrdofoil and became stranded in shark-infested waters revealed to the Daily Mail how his Apple Watch saved him.

John Zilles was about 1.6km offshore near Ventura, California when he crashed and was unable to get his kite working again.

Stranded in the water with a great white shark nursery nearby, Zilles used his Apple Watch to call the coastguard.

"I had a huge wipeout, and my hydrofoil skated away from me.

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"As I was swimming away, my kite fell down, and because it was a calm day so I couldn't get it to fly again.

"Suddenly I was a mile offshore and my ride was over," Zilles told the Daily Mail.

After spending at least 20 minutes trying to get his kite to fly again, he started swimming towards shore.

While he was making his was to land, Zilles went to check the time on his phone and remembered he could make calls on it.

"I was really surprised that I had a strong signal, so I called my kids, and said 'don't worry, I crashed and I'm swimming to shore, and will be home late'.

"I then called my son back, and asked him to send me the number of the Coast Guard, just in case."

Zilles continued to swim for another 30 minutes before becoming paranoid about the sharks in the area.

"I started thinking about all the great white shark sightings in our area, and although I realised I could probably swim in, I couldn't stop thinking about sharks - it was a real mind bender.

"It was maybe a two-hour swim, so I probably had another 90 minutes - but there was a strong current and I had a lot of gear as well, so I was only kicking," he said.

He decided to call the Ventura Harbour Patrol and ask for help, explaining his situation.

Officers sent out a boat to collect him, asking Zilles to call them back when he saw the boat.

"15 mins later I spotted the boat - I had to call them as it was going to wrong way.

"So I called and asked it to turn 90 degrees and go 400 yards forward - and they found me straightaway," he explained.

After being rescued, Zilles was so impressed that he contacted Apple CEO Tim Cook to tell his story and got a reply reading, "Wow. Happy to hear you are safe."