John Craig, a 34-year-old British diver, swam about 7.5 km (4.5 miles) in a desperate attempt to escape a giant shark that was following him all the way to the shore, media reported.
The young man found himself one-on-one with a huge tiger shark after his boat was swept away due to engine problems.
"It [the shark] was extremely close and curious and kept approaching me from different angles. It was trying to work out what I was and whether I could be on the menu," the man told the BBC.
When he finally made it to the beach near Shark Bay, he was spotted by a local rescue team.
"It's an absolutely incredible story," Shark Bay Volunteer Marine Rescue commander Greg Ridgley told Perth's Sunday Times. "He swam at least 5 miles in shark-infested waters, I just can't believe anybody could do that."
Tiger sharks are notorious for their aggressive attacks on humans, which in most cases end fatally.