Potocka, 21, was seen wearing an oxygen mask as she was taken away for medical attention. Medical personnel at the pool said she was conscious.

Potocka collapsed as she got out of the water and almost immediately was surrounded by a half-dozen medical attendants who put her on a stretcher after about a minute and carried her off the pool deck. It was not clear if she received CPR.

Israeli swimmer Lea Polonsky, who swam two heats after Potocka, said swimmers know their sport has inherent risks.

“Of course, that's something in the back of your mind, but we do every day push ourselves to the limit,” she added.

“You always know something like that can happen. It's not something you think about during the race, but it's always there.”

This is Potocka's first Olympics. She resides in the Slovakian capital of Bratislava.

Potocka finished seventh in her heat in two minutes &14.20 seconds. Her time was not fast enough to advance her to the event's semi-finals, which eliminated her from the competition.