Acclaimed director James Cameron has revealed that his movie "Avatar 2" will feature underwater scenes.

Cameron has officially moved the stage of "Avatar 2" from development to principal photography, meaning production and shooting are now underway. The 63-year-old director has also detailed the challenges involved in shooting for the sequel to 2009's science fiction (sci-fi) film "Avatar," where he stated that the most challenging complications involved underwater scenes. These scenes will reportedly be taking place in sunken areas in the fictional planet Pandora.

"It's never been done before and it's very tricky because our motion capture system, like most motion capture systems, is what they call optical base, meaning that it uses markers that are photographed with hundreds of cameras," said Cameron.

He added, "Basically, whenever you add water to any problem, it just gets ten times harder. So, we've thrown a lot of horsepower, innovation, imagination and new technology at the problem, and it's taken us about a year and a half now to work out how we're going to do it."

This is also one of the reasons why the release of "Avatar 2" will not be happening until the year 2020. Cameron hopes that with this revelation, he can now answer fans who might be wondering what's taking the sequel so long.

Cameron has also stated that despite the current technology today, the only successful underwater camera scene occurred just a week ago, meaning the problem with underwater camerawork was not resolved before filming began back in September.

To add to the complications, the cast of "Avatar 2" is relatively young, so the production crew reportedly had to train them on underwater acting for six months.

Fans will find out how the scenes will look like once "Avatar 2" arrives on Dec. 18, 2020.