A terrifying GoPro video shows a 16-year-old girl and her father swept out into the ocean by a riptide off the shores of Nantucket.

In the video, the pair are fooling around in the water when they realize they're being pulled away from shore -- and can't swim back. Derrick Johns and his daughter, Erynn, start trying to make their way back to the shore, but struggle in the waves.

Amazingly, the pair is able to use the GoPro stick to stay together as the current pulls them out, which might have saved one or both of their lives. On the video, you can hear their voices screaming, "I can't!" and "Come on!" as they fight the current.

Derrick Johns, a former Marine, reached a shore in a semi-conscious state and required medical attention. Erynn, a high school soccer player, managed to walk out of the water on her own.

Erynn's mother, Jennifer Johns, was briefly caught in the riptide as well, but a bystander on the beach managed to reach her and pull her to safety in time.

"I was a Marine, and I've been in some pretty harrowing situations," Derrick Johns told The Boston Globe. "That one was the scariest, because it wasn't just me, it was my wife and daughter."

The Globe reports that it's a particularly bad year for riptides at Nantucket. A typical summer might only have 55 rescues, but since 135, the beaches have seen 135 such incidents.

The clear message: Stay out of the water.

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