Finally tonight a teen's adventure caught on tape. Out at sea last saturday he decided to go surfing on the world's biggest shark. The video has gone viral. The teen explained to us why he tried the... See More
Finally tonight a teen's adventure caught on tape. Out at sea last saturday he decided to go surfing on the world's biggest shark. The video has gone viral. The teen explained to us why he tried the risky stunt. Matt gutman has the story. Reporter: To chris kreis it loomed like a titanic boogie board, an endangered whale shark, the world's biggest fish, as long as a school bus, as heavy as a sherman tank. We drove right back up to it and noticed that he was feeding. Reporter: Swallow volkswagen sized size gulps of water and tiny fish off florida. I decided you know that, maybe I should go try and swim with him. I might not be able to do it ever again. Reporter: And so he did. There's the 19-year-old latching on. It was almost like an adrenaline rush. Reporter: Whale sharks are considered the gentle giants of the sea. But after nine seconds he knew it was time to let go. He began to descent and if something doesn't want you on it you might as well just let it go. Reporter: Human encounters with sea creatures are often inspiring, as I discovered with pod of tlifk dolphins. But touching or harassing the wrong animal in florida, can get you arrested. Reporter: This man posted a facebook picture of himself manhandling a manatee and was promptly busted and this bozo -- should definitely have been arrested. After this woman tried riding one of these creatures, she turned herself into police. While riding sharks is certainly not illegal, memorable. Still, maybe once and only ride for chris.
This transcript has been automatically generated and may not be 100% accurate.