The Slovakian swimmer Tamara Potocká collapsed and needed first aid, before being rolled out on a stretcher with an oxygen mask, according to AP.
Potocká participated in the women's 200 meter medley, and fell apart when she came out of the pool.
The 21-year-old was quickly surrounded by medical personnel and was on the stretcher about a minute after the collapse. Then she could be taken away for further examination.
Medical personnel on site said that Potocká was conscious when she was rolled away on the stretcher.
The Slovakian finished seventh in the heat after swimming in 2.14,20, which was not enough to advance from the qualifying round.