Rob Marshall was challenged by underwater scenes on The Little Mermaid

Rob Marshall was daunted by the underwater scenes on 'The Little Mermaid'.

The 62-year-old director has helmed the live-action remake of the Disney animated film and had to draw on all of his previous experience behind the camera to shoot the watery sequences required for the flick.

Rob told ComicBook.com: "It was definitely daunting and a challenge. I mean, as I started, I thought, 'What have I gotten myself into?' But I have to say, if I hadn't done all my movies prior to this, I wouldn't have been ready for this one because it was so complicated.

"I mean, everything had to be choreographed in advance so that we could actually take all of that information and give it to our stunt team."

The 'Chicago' director continued: "All of the underwater work was literally done on rigs, you know, apparatuses, wires. And sometimes in one scene, you know, many times in one scene, they'd say two lines. I'd say 'Cut', and we'd put on another apparatus for a couple more lines. It was all done in little pieces, like a mosaic for even just one scene."

Melissa McCarthy - who stars in the film as antagonist Ursula - admits that she was blown away by how "technically impossible" the underwater scenes seemed to be.

The 'Bridesmaids' actress said: "I've never seen anything look like that. I just can't process how technically impossible that seemed to be and how you never thought about it, just watching you're like, 'Of course, I'm underwater.'"

Melissa added: "Every hair is digital, all the movement. You know we each had, what, like seven, eight people that were a part of our team to help keep that kind of undulating. It took a lot of people to make it look so effortless."