Daisy Ridley completed rigorous training for Young Woman and the Sea

Daisy Ridley underwent a gruelling training regime for 'Young Woman and the Sea'.

The 32-year-old star plays the lead role in the biopic about Gertrude Ederle, an American swimmer who became the first woman to swim across the English channel in 1926, and spent months completing intense training in the Black Sea for the film.

Daisy told Deadline at the movie's premiere: "I was really alone in the Black Sea, and I was really trying to keep pace with the camera.

"And then I was trying to keep pace with the boat and the camera boat. I trained for three months and then we were training during filming."

The 'Star Wars' actress added: "And then we did the big swim at the end. So it was nine days in the Black Sea. It was overwhelming. It was cold. Each time, it was scary."

Daisy explained that she realised that all her hard work had paid off when she got to witness the finished movie.

She said: "You can see that it's the open water. You can see that I'm there, and it adds to the majesty of the story. And also, it's just a tiny part of what Trudy did, which is crazy."

Director Joachim Ronning paid tribute to Ridley's commitment to her portrayal of Ederle.

He said: "Nothing could really prepare her for what we did week after week out in the open ocean, sixty degrees water, her lips blue. (She) never complained and always going for it, always getting it, channelling Trudy... And I hope the audience can feel that."

The Norwegian filmmaker continued: "It was very important to me to shoot it on real water. I wanted to be in the elements and tell this story. I didn't want to be in a tank with a blue screen or green screen."