American artistic swimmer Anita Alvarez said she was "shocked" when she saw the "beautiful" AFP photographs showing her sinking unconscious to the bottom of the pool and being rescued by her coach at the World Swimming Championships.

Alvarez fainted and dropped to the bottom at the end of her individual routine and was saved by her quick-thinking coach. AFP's underwater robot camera captured astonishing images as the drama unfolded.  

Alvarez, who was unconscious throughout, told Spanish media she was moved when she saw the images.

"At first I was shocked," she said.

"I didn't expect something like this to be published. But then I took it in my stride. I didn't want to look at it negatively. 

"Now I think the photos are beautiful, in a way. To see me down there in the water, so peaceful, so quiet, and to see Andrea coming down with her arm outstretched trying to reach me, like a superhero."

When she saw Alvarez sinking and lifeguards standing watching, coach Andrea Fuentes, dressed in shorts and a T-shirt, dived to the bottom of the pool and dragged Alvarez to the surface.

"It was a big scare. I had to jump in because the lifeguards weren't doing it," Fuentes told Spanish media.

"When I saw her sinking, I looked at the rescuers, but I saw that they were stunned. They didn't react.

"My reflexes kicked in.

"I think she was at least two minutes without breathing because her lungs were full of water," said Fuentes, a four-time Olympic artistic swimming medallist, adding that the swimmer's heart was beating.

Alvarez said the photos also reinforced her love of her sport.

"Sometimes the most peaceful place on earth is underwater: when you sit at the bottom of the pool in silence. You feel you are weightless, you are with yourself. I love that. Sometimes I need that moment. And in the photos it all looks very natural."

The USA artistic team released a statement from Fuentes on Thursday saying Alvarez had fainted due to the effort expended during the routine. 

"This happened to her once last year at the Olympic Qualification Tournament when competing her duet," said Alyssa Jacobs, a spokeswoman for the US team.

Jacobs said Alvarez could still take part in the Team Free Final on Friday.