Chris Kreis was fishing in the Gulf of Mexico when he came across a 30-foot, 50,000 pound whale shark. The 19-year-old didn’t hesitate. He jumped in and rode it.

"It's massive, it's the size of the boat," Kreis told ABC 7. The Fort Meyers teen rode the fish for 20 seconds and posted a video of his ride on YouTube.

Whale sharks are the largest fish in the sea, and can reach lengths of 40 feet or more. While the name “shark” has negative connotations, the fish is a gentle giant that mostly eats plankton. According to National Geographic, the massive fish allows swimmers to ride it on occasion, but the species is vulnerable. It’s hunted in parts of Asia, including the Philippines.

"When I started holding on I felt the whale shark it started moving itself, it felt the drag and it didn't really want me on there so I let go and that's it," Kreis said.

Although Kreis’ ride isn’t illegal, marine biologist Bruce Neill warns the giant fish could have been injured.

"When people spend a lot of time and pressure on a fish it takes away a slime that covers the fish. They need that layer to stay healthy,” Neill said.

At the end of May, whale sharks sightings have been reported in the Gulf of Mexico. Scientists have been collecting reports to look for patterns of their movements off the Florida coast, The Herald-Tribune reports. A 26-year-old scuba diver spotted a whale shark 30 miles off the coast of Naples, Fla.

"It felt like I was dreaming, not real," Bill D'Antuono, told NBC 2. "Everyone that dives, that I talk to, they want to see a whale shark. I was lucky enough to see it."