Fuentes dived into the pool to rescue American Alvarez who passed out at the end of her solo free routine in Budapest, Hungary.
"I had to pull one of the humans who I love the most out of the water, and fight for her to breathe," USA Coach Fuentes told Olympics.com in an Instagram live with @Olympics on Thursday (23rd June 2022).
"I saw it almost before it happened. I’m used to seeing them every day, 8-hours a day, more than my kids," she added, "I noticed that when she was doing the last part of the routine her feet were a bit more pale than usual.
"When she finished, instead of going up [for air], she went down... so I knew it was not ok. I wanted her to be safe as fast as possible, and went as fast as I could.
"I grabbed her and brought her to the surface."
Fuentes highlighted that it's something she and others are trained to deal with, and often have to use those skills in practice sessions.
"I’m a lifeguard so knew exactly what to do. The heartbeat was there so it was fine.
"I saw everyone helping and trying to help, that was beautiful.
"It’s not the first time it happens in our sport. It happens many times in practice. When you hold oxygen it's one of the after effects."
The 25-year-old competitor was quick to recover following the rescue, according to the Spaniard, who won four synchronised swimming Olympic medals in her own career.
And the coach described Alvarez as a "badass woman" after the American said she wanted to compete in Friday's free team finals.
"Anita woke up today, saying, “Andrea, I’m going to swim," Fuentes continued, saying the athlete had spent the day with the team doctor, who had cleared her to compete, but the final decision was being taken after a consultation with the rest of the team.