"I woke up out of sight of land," the actor, 84, recalled, according to a report in the U.K.'s Guardian newspaper. "I started paddling with the swells and I started seeing fins swimming around me and I thought 'I'm dead!' "
Thankfully for Van Dyke, the circling fins didn't belong to creatures with sinister – or hungry – motives.
"They turned out to be porpoises," Van Dyke said. "And they pushed me all the way to shore."
For any doubters, Van Dyke stresses, "I'm not kidding."
Van Dyke also shared the story on a visit to The Late Late Show with Craig Ferguson recently. Watch him discuss it below. (Skip to 8:30 to see the story.)