Chief Meteorologist Ginger Zee put on a demonstration to show how swimming in a pool and swimming in open water are two very different things.
First, three college football players and two elite dancers from Temple University were put to the test in a pool.
They had to swim four lengths of a pool -- or a hundred meters -- without touching the bottom.
Then they headed to Ocean City, New Jersey, to do the same distance in the ocean.
They said it was a truly sobering experience.
Experts say they want everyone to see that, as fit as you may be on land, the ocean and other kinds of water are different environments.
For more, watch the video above.