"It was a big scare. I had to jump in because the lifeguards weren't doing it. I was scared because I saw she wasn't breathing, but now she is doing very well," Fuentes told Spanish publication MARCA.
"Anita is [doing] much better."
Incredible underwater photos captured the frightening episode.
It is not the first time Alvarez has fainted in the water. At an Olympic qualifier in Barcelona last year, she lost consciousness during her artistic swimming routine.
"Unfortunately, I've seen it happen to her before," Alvarez's mother Karen told WIVB after that incident in Spain.
"Never in competition, though. I knew right away. On their last element, I could tell something was up.
"It was hard to watch, definitely."
A fully-clothed Fuentes dived in to help on that occasion too.
The current competition in Budapest represents Alvarez's third trip to the world championships. She ended up finishing seventh, while Japan's Yukiko Inui won gold.
