Mike Colonna, 29, of Chicago told WBBM-AM, Chicago: "This is a little scientific experiment. I haven't trained at all. So I'm going to see if I can do it. And then after that, I'm done putting forth physical effort and exertion."
Colonna said he rides his bike to work, and that's about all the exercise he gets.
"I don't think the human body is a house made of glass," he said. "I think that if you push it, you can do whatever you want if you put your mind to it. So I'm going to finish."
Colonna did finish, in a little more than five hours, 52 minutes.
Swim Week Miami Beach 2014 [PHOTOS]