Naomi Watts on Preparing for 'The Impossible'

P yo you kn you know, she once played king kong's girlfriend. Ap and naomi warand naomi watts is still reaching new heights in hollywood with a career built on gutsy performances. Her latest movie... See More

P yo you kn you know, she once played king kong's girlfriend. Ap and naomi warand naomi watts is still reaching new heights in hollywood with a career built on gutsy performances. Her latest movie conjures up the epic title waive, but for one family on vacation, the tsunami of 2004 was a test of survival and the fierce determination of a mother's love. Abc's bob woodruff talked to naomi watts for tonight's "nightline" interview. Reporter: It started out as an idyllic vacation for a young family on the west coast of land, a mother and father played by naomi watts and ewan McGREGOR AND THEIR THREE YOUNG Sons. But the holiday soon turns to a living held. And an epic fight for survival in the most devastating natural disaster in modern history. IT WAS DECEMBER 26th, 2004, WHEN A giant tsunami swept across southeast asia, destroying entire villages, killing hundreds of thousands. "The impossible" tells the whole story in excruciating detail of what happened to one family caught up with millions of people in the disaster. I will find them, I promise you that. It just felt like it was rooted in real truth. Like every line of dialogue, every detail, everything just felt real. Reporter: Naomi watts plays maria, who along with her son lucas, barely survives the initial wave. Maria was badly injured. I'm scared. Reporter: Facing unimaginable obstacles, she needs her oldest son to help her and others. She was sure that she was going to die. And so it was absolutely vital to her to impart this need to take care of others. We are almost there. We have to get to safety. We have to help that boy. Reporter: The tsunami killed more than 200,000 people and left millions homeless. For those of us covering it, it was one of the most horrific scenes we had ever witnessed. The entire neighborhood as far as the eye can see is completely wiped out. To capture the horror of the event, the director didn't rely solely on computerized special effects. Instead, building a huge water tank filled with rushing water and debris. We were truly in an uncomfortable situation, which was a massive water tank, being thrust one way, water coming this way, water coming behind you, side pumps, debris, garbage, everything thrown at you. Reporter: The real family the film is based on are from spain. Lucas is now 18 years old. And maria was deeply involved in the production of the movie. We spent hours talking to each other. I wanted to get I her mind, every moment that took place in these 48 hours. Reporter: In thailand, they filmed in the exact hotel, now rebuilt where they were staying when the tsunami hit. Real survivors are in the movie as extras. Did you have a chance while you were there in thailand to talk to some of those who survived that moment? Yes, lots. We were around it every single day. Where you're on the set or back at the hotel, there were always reminders of it because everybody was connected to it in some way. Reporter: Watts has very few speaking lines, she says only two pages worth, and conveys all of her emotion in other ways. Watts has never shied away from tough roles. Don't touch me! Get out of my house now! Reporter: In "21 grams." She wasn't always in demand. I was doing endless auditions for years and getting rejected over and over again and really taking a beating on my soul. Reporter: She landed a role in "mulholland drive" at age 31, old by hollywood standards. People said overnight success after "mulholland drive." I went overnight? That's a long night. Reporter: Now 44, she is still getting prime roles in hollywood. I feel like the roles are better for women at this age. There's just more than what i girlfriend would be. Reporter: And there is real buzz over a role she's about to play. Princess diana. This is a story about a woman who was both complicated, full of contradictions. Someone who was fighting for happiness and forced into isolation. Reporter: In real life, she is happily living with her partner actor liev schreiber and their two sons. We talked at the top of the crosby hotel. Not far from their downtown home. I've grown to love new york. It's not an easy straight away. It takes time to get used to this concrete jungle. Reporter: In february, she might be heading to los angeles for the oscars. There's some buzz out there that it's got a good shot. Well, that's nice buzz. Reporter: It's not one you can ever deny. Well, it's always nice, the idea that your peers will recognize you. But it just makes me go all sweaty and clammy and get nervous. Reporter: For now, watts is staying focused on what happened on that beach in thailand, and the lessons of hope and survival that their story imparts. I'm bob woodruff for "nightline" in new york.