Barnes, 20, says she went to collect coral samples around 4 a.m. on Friday, and after she began cramping, was pushed out to sea.
She says she knew they were supposed to always swim with a buddy, and that she had "for the first couple weeks," but thought the small bay was calm enough to snorkel alone.
Barnes was stranded for 16 hours, mostly spent treading water as the sun beat down on her face and jellyfish swarmed around her legs.
"Even when I didn't feel like I was strong enough," Barnes said, her legs were able to just keep going. "It didn't seem like a choice."
Fellow students and school staff soon realized Barnes was missing, and organized a search. They also called on the help of Senator Marco Rubio and Congressman Vern Buchanan, both of Florida, to reach out to the Honduran government.
Barnes was eventually able to swim back to shore, where two people gave her water and used their kayak to take her back to where she was staying.
Barnes is now back in Florida, where she is recovering from jellyfish stings and sunburn.
Notable deaths of 2014 [PHOTOS]
UPI Almanac for Tuesday, Sept. 30, 2014