The King Kong star appears opposite Ewan McGregor in the new disaster epic, which tells the story of real-life survivor Maria Belon struggling to find her family in Thailand in the aftermath of the 2004 Indian Ocean tsunami.
Most of the ocean scenes were filmed in a special tank in Spain, but Watts admits the shoot didn't go smoothly for her and she was left terrified when the equipment failed.
She tells entertainment site AwardsLine.com, ""Working with water is one of the more difficult things to do on film, and it certainly lived up to its reputation...
""The underwater stuff was incredibly difficult, and I did not like that at all. It's always nerve-wracking holding your breath... But we were anchored into a chair (with) weights on us to keep us down. You had the oxygen tank right there up until (the cameras) rolled, and you'd push it away and then the chair starts spinning, and you have to do all your arm-acting and head-flipping. There was one point when I was about to get out of the chair, and I couldn't get out. It was a technical problem, and it really freaked me out.
""I remember being really angry when I came out of the water because it just made me panic, and that's the emotion that came out of me.""