Having conquered humans en route to 23 Olympic gold medals, Michael Phelps pursued steeper competition by racing a shark.

On Sunday night, Discovery Channel will air Phelps' quest to out-swim the animal as part of its annual Shark Week. For obvious safety reasons, he swam with a cage and safety divers at a different time than the shark.

When discussing the upcoming event on The Tonight Show Starring Jimmy Fallon, Phelps recalled telling his wife he wanted to do the stunt without a cage.

"She said, 'Well, we have a family. I don't know if that's really gonna fly.'"

Phelps shared his shark obsession and the challenge of getting one to swim in a straight line. He also described the "awesome" experience of nearly coming nose-to-nose with a great white while cage-diving.

According to ThoughtCo.'s Jennifer Kennedy, a shark can swim 12 mph—in attack mode. At least the cage eliminated that possibility. ESPN.com previously recorded Phelps' peak speed at 6 mph.

[The Tonight Show Starring Jimmy Fallon]