'Avatar': Kate Winslet and Sigourney Weaver on Filming Their Record-Setting Underwater Scenes (Exclusive)

Kate Winslet beat Tom Cruise's previous record while filming scenes for 'The Way of Water.'

In director James Cameron's highly anticipated Avatar sequel, The Way of Water, Kate Winslet joins the franchise as a pivotal new character, Ronal, a free diver of the Metkayina. And in doing so, the actress set a new record for holding one's breath underwater while shooting scenes for the new movie, which will transport viewers to parts of the planet Pandora that were not seen in the first film.

While Winslet is proud of the achievement, which shattered a record Tom Cruise set while filming Mission Impossible: Rogue Nation, it's something that required "a lot of training," she tells ET's Nischelle Turner about holding her breath for nearly seven minutes. "It's a lot of learning about the safety and what you have to do to get your body to adjust and adapt to be able to do that." 

"It certainly wouldn't have been possible for me to hold my breath for that long at depth, so there were surface static breath holds that we were doing to improve your skills," she explains. "It's a physical shift and it's something that you have to learn how to do. But at the same time, it's also a mindset in terms of quieting your mind, slowing everything down. So, quite honestly, my breath holding was done during our training time." 

And it was during that time, "I would just, like, hang there in the water," she says, revealing that she'd "count the slats. I'd go over it again. I'd make lists in my mind. But you have to be careful not to make, like, too many comprehensive complicated lists 'cause that also takes brain power. Like, it’s a whole, like, zen thing, actually. It’s completely amazing." 

And Winslet wasn't the only one to outdo Cruise, with Sigourney Weaver, who returns to the franchise as a new character, Kiri -- Jake and Neytiri's (Sam Worthington and Zoe Saldana) adopted teenage daughter -- also holding her breath for six and a half minutes. 

"I think it was a huge surprise," Weaver says of her own, unexpected moment achieved while filming the underwater scenes, especially considering that on her first day of training she held her breath for a minute. "It is an acquired talent." 

"Well, you know, the whole idea was quite challenging, I think for all of us." she says, revealing that they worked with a trainer who teaches Navy Seals for a year as they learned how to hold their breath for longer and longer. "We had to spend long days underwater. So, when I watched the film, I was astonished by how comfortable we looked in that element." 

20th Century Studios

And that was especially important because she plays "a character who falls in love with the water as she does in any natural environment," Weaver says, with Cameron pointing out that Winslet's character "was meant to have been born in water and lived in the ocean her entire life." 

Even though Saldana had worked on the first Avatar film, this one was a whole new challenge. "Once again, it's like back to Pandora. Back to working with Jim and this wonderful cast and discovering new things that I am capable of," she says. "I challenge myself the way Jim challenges himself." 

But once she also mastered the technique required to hold one's breath for an extended amount of time, she was excited to know how to do it. "It was an exhilarating tool to obtain," she says. 

While the cast all met Cameron's challenge -- and helped him achieve a visual spectacle that shows life underwater in a whole new way -- the director says it wasn't all about the technical achievements, which also included free diving for some of them. 

"First of all, we didn't cast anybody in this movie because they could hold their breath. We cast them because they were the right people to play the character," the director says. 

"What I’m most proud of is how the actors’ performances came through so resoundingly in characters that are CG, you know. They’re not human characters," he explains. "And we like to not do it with makeup 'cause that would’ve looked horrible. We do it a whole different way, so it has this kinda magical quality of them looking extremely real but they’re kinda ones and zeroes."  

Avatar: The Way of Water opens in theaters on Dec. 16.