Take a look behind the scenes of 'Avatar: The Way of Water,' including the giant tank where James Cameron filmed much of the movie

It still has a ways to go to catch its predecessor, 2009's "Avatar," which is the biggest movie of all time with $2.9 billion at the worldwide box office, but it's showing strong legs.

The success of "Avatar" kickstarted a 3D boom in the early 2010s. But Cameron thinks it didn't last because movies were converted in post-production.

"I think the studios blew it," Cameron told The New York Times. "Just to save 20% of the authoring cost of the 3D, they went with 3D post-conversion, which takes it out of the hands of the filmmaker on the set and puts it into some postproduction process that yielded a poor result."

Some have criticized the technique, including The New York Times' Ben Kenigsberg, who called it "unnerving" in non-action sequences.

But "The Way of Water" has for the most part been praised for its visuals, especially compared to most other modern-day blockbusters. A Vox headline declared that the movie "reminds us that blockbusters don't have to look absolutely terrible."

Much of the movie takes place in the oceans of the fictional planet Pandora. The tank had wave and current machines to better recreate the underwater action of "The Way of Water," according to The Los Angeles Times.

The cast told The New York Times in a story published in October that Kate Winslet held her breath for seven minutes during filming, a new on-set record.

When asked why he insisted on the actors doing this, Cameron responded: "Oh, I don't know, maybe that it looks good? Come on!"

"You want it to look like the people are underwater, so they need to be underwater," Cameron said. "It's not some gigantic leap — if you were making a western, you'd be out learning how to ride a horse."

The crew first experimented with rigging actors in the air on wires while wearing motion-capture suits, to simulate motions in the water. But Cameron rejected it without even seeing a test, according to The Los Angeles Times.

When pivoting to actual underwater filmmaking, they "quickly found out that the infrared gets absorbed in water, which is normally how we do motion capture, so we had to go to ultraviolet light ... that would transmit through water but would also be picked up by the camera sensor," production supervisor Ryan Champney told The Times.

In the time between "Avatar" movies, Cameron broke the record for the deepest solo dive in history in 2012, when he traveled to the deepest part of the Mariana Trench — seven miles down, called the Challenger Deep — in a specialized, state-of-the-art submersible.

He even joked in 2018 that he makes movies like "Avatar" to fund his deep-sea explorations.

"Some people think of me as a Hollywood guy … (but) I make 'Avatar' to make money to do explorations," Cameron told The Daily Telegraph.