Underwater acting 101: Avatar 2 cast explains how they pulled off extreme free diving

In some ways, Stephen Lang had it easy compared to his castmates on the set of Avatar: The Way of Water. Unlike Sam Worthington, Zoe Saldana, Sigourney Weaver, Kate Winslet, as well as others, Lang's character didn't spend all that much time in the water.

"If he is in the water, he'd really like to get out of the water," Lang tells EW of Col. Quaritch, who returns in a much different capacity in the sequel compared to the 2009 original. "He's never in there by choice, whereas there are many characters in this film who are water creatures. That's where they exist."

In order to pull off the underwater sequences while maintaining director James Cameron's chosen method, performance-capture, the majority of the actors trained in the ways of free diving, a form of diving that relies on breath holding and not scuba gear. Cameron himself has been free diving for years.

It turns out, Lang was pretty darn good at it regardless of the needs of Quartich. "I did fine," he says, modestly. "I can hold my breath in a static hold for probably five or six minutes. When I'm working, I can do a minute, minute and a half underwater when Jim says action, so I get the work done."

Avatar: The Way of Water picks up years after the events of Avatar, after the RDA has returned to colonize Pandora. Jake Sully (Worthington), now a prime target, flees with Neytiri (Saldana) and the rest of his family to seek refuge with the Metkayina, a tribe of Na'vi whose bodies have adapted to ocean life.

The cast studied free diving with Kirk Krack, who's achieved global recognition for his diving expertise and his jaunts in extreme underwater environments. Winslet became a quick standout as it was widely reported the actress, who plays spiritual Metkayina chieftain Ronal, could hold her breath past seven minutes.

"I think anything to do with water, it's 10 times harder, whether you're under it or whether you're being drowned, sinking in it," Worthington says. "The real challenge on this one was trying to preserve your character while you're doing these things in water, because you could quite easily get caught up in your own head, which then takes you out of the scene, which takes you into your own fears, and then you're not doing your job."

Weaver, who plays Jake and Neytiri's adopted daughter Kiri, would always arrive to set about half an hour before the others. She and her husband, Jim Simpson, trained with Krack together, and breathing became her central focus. It's similar to how the characters themselves describe it in the film: breathing deeply to take control of your heart rate before diving under.

"My husband's from Hawaii, so he's like part seal," Weaver says of Simpson with a laugh. "What he said to me once we got in the tank, he said I always experienced a kind of apprehension. Would I be able to do this? You don't want to keep Jim waiting while you pull yourself together, so I'd always get to the set about 20 minutes earlier than I was supposed to and just get the gear on and do the breathing process, which really calms you down and is a wonderful transition zone where you give up your mammalian instinct to stay on land and become half fish."

For a quick fix, Weaver praises Rescue Remedy, which is pegged as a natural stress and sleep support, that she took to help ease her nerves.

Saldana says she leaned heavily into the training with Krack, paying close attention to every detail. "I was making these small, little discoveries about myself. It's like, 'Oh! You have it in you.' There's serenity past the panic," the actress says. "The day of, you wake up and you tell that motherf---er that lives in your head, that is looking to sabotage everything that is meaningful to you, 'Hey, I'm gonna take the wheel today.' By the time you're in the water, you need to leave that MF in the trailer."

Jack Champion and Trinity Bliss have more cosmetic tips for underwater acting. Champion, who plays Spider, a human child and friend of the Sullys, says to "keep your face relaxed."

"That was a big one," notes Bliss, who plays the youngest of Jake and Neytiri's children. "Keeping your face relaxed and, obviously, not like a pufferfish."

Another tip? "Keeping your lips a little parted because it just adds more motion to camera," adds Champion, "and also lets water into your mouth."

Avatar: The Way of Water is now playing in theaters.

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• The future of Avatar: How The Way of Water sets the stage for a new Na'vi era
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• Avatar: The Way of Water review: A whole blue world, bigger and bolder than the first