Cast members got scuba certifications and trained with a free-diving instructor, and the movie’s sound mixer kept four microphones constantly running in the tank to capture underwater background noises.

Source: https://www.nytimes.com/2023/01/13/style/avatar-bathroom-break.html

Environmental consultant and university student Bridgette O’Shannessy, 32, was attacked by a great white while free-diving off a reef on Friday afternoon.

Source: https://www.perthnow.com.au/news/sharks/south-australia-shark-attack-bridgette-oshannessy-survives-terrifying-white-pointer-encounter-while-diving--c-12522235

He runs a free-diving school in Moscow and judges the sport, in which divers shun oxygen tanks and hold their breath underwater.

Source: https://www.perthnow.com.au/news/world/four-astronauts-lift-off-to-replace-space-station-crew-c-11712099