As he often does, John "Les" Brierley set out to go for a solo dive in perfect conditions on Sunday, this time at the famous SS Yongala dive site off Queensland, Australia. Fortunately he alerted a colleague of his plans.

When the 68-year-old surfaced from his dive, he realized the strong current had swept him away from the dingy he tied to the site's mooring. Thus began a harrowing episode for Brierley being lost at sea for more than 17 hours.

"I used all my energy trying to swim back to the yacht and the mast was growing shorter and shorter all the time," Brierley told the Australia Broadcasting Corp. "Eventually I thought 'I'm just using energy' and my legs were cramping up really badly so I just had to drift."

Brierley was further dismayed when he reached for a device that could help rescuers find him immediately.

“To cover myself I always carry a personal locator beacon in a weatherproof case on my tank so I thought now is the time to set the PLB off so I opened the case and it was empty,” he told The Sydney Morning Herald.

Brierley had taken the device out to clean it a few days before and forgot to put it back in its case on the tank. Brierley then began thinking about how he would die.

"I was debating in my mind, which would be the preferable way to go, to drown or get eaten by a shark?" he told 7 News.

His attempt to flag down passing vessels proved futile.

“One cargo ship went past…I thought they’d seen me, I was waving my fin because you are a hard thing to see in the water with a bit of a swell running…but they just kept sailing,” he told the Herald.

“Then three trailer ships came by in the nighttime and the only way I could signal them was to use my camera light that has a big strobe on it [which didn't work either].”

Leaving his dive plans with someone ultimately saved his life.

RELATED: Scuba divers rescued after 48 hours adrift; sharks circled them

When Brierley failed to check in with her at the predetermined time at 5 p.m. on Sunday, Jillian duBouis raised the alarm with the Coast Guard and a rescue mission was launched.

At noon the next day, rescuers in a search helicopter spotted him 30 miles from his boat. Police told the Herald it was like finding a "needle in a haystack."

"I was waving [at them] and I thought, 'They gotta see me now,'" he told 7 News. "It was such an awe-inspiring moment when that smoke bomb dropped next to me, to know it was all over, you know?"

Brierley said he would continue with his solo dives but will make sure he has his locator beacon with him.

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