Oscar-winning actress Kate Winslet is apparently back in the water in a big way in the upcoming Avatar sequels. While Winslet first broke out with films like Heavenly Creatures, it was James Cameron’s mega-hit Titanic that catapulted her to superstardom—but making the iconic historical epic was no cake walk. Given the sheer amount of water necessary to shoot Titanic, and the amount of time actors Winslet and Leonardo DiCaprio had to spend in said water, there have been many stories recounted over the years of just how arduous an experience it was getting all of those scenes on film. But for her reunion with Cameron on the Avatar sequels, it appears that Winslet took to the water like a fish.

Producer Jon Landau recently shared some insight into the making of the Avatar sequels while attending a Collider-hosted IMAX Q&A for Alita: Battle Angel, and while talking about the long-anticipated underwater sequences for the films, he revealed that Winslet got to the point where she could hold her breath underwater for nearly seven minutes:

“We built a water tank that was 500,000 gallons of water, and we are doing performance-capture under the water, on the surface of the water, and above the water. We trained our cast to free-breath-hold, because in the sequences they have to just be swimming, they can’t be on scuba, and they have to be able to do long takes. So we had a gentleman named Kirk Krack come in and train everybody that needed to be underwater how to go underwater and how to hold their breath. Kate Winslet had to train in this and she got up to a static breath hold of just about seven minutes. It’s amazing, it’s mind over matter. You see Kate going underwater and she just felt so comfortable. There was one day, we have a tank where she was just rehearsing and testing and we have some windows into it, and I go in there and she’s just walking on the bottom [of the tank] left and right, left and right, left and right, then she sees me in the window and she just waves. I couldn’t believe it!”

That’s some Oscar-level lung capacity there. Winslet fills the role of Ronal, a free-diver of the Metkayina clan—likely the clan that lives on or under the water.

For more on the Avatar sequels, click here for what Landau had to say about the geography and upcoming live-action filming that will be taking place in New Zealand. Watch the full IMAX Q&A below.