During the scene where the girls are on the beach checking the wave conditions, the man that comes out of the water with the bloody eye was an actual surfer who got hurt. The film crew shot it and later obtained permission to use it in the film.
The rainbow behind Kate Bosworth at the end of the competition was real. It was almost edited out because it was too cheesy, but since Hawaii really does have frequent rainbows it was left for authenticity.
For the big competition scene, a male pro surfer was used, complete with wig, bikini and shaved legs. But in the final edit, he was digitally replaced with Kate Bosworth, with only his feet remaining in the film.
Kate Bosworth was briefly knocked unconscious while filming one of the surfing lesson scenes. Matthew Davis tried pushing his surfboard vertically underwater, it slipped out of his hands, launched into the air, and struck Kate on the top of her head. She was taken to a local hospital as a precaution but suffered no permanent injury.
Former surfing world champion Tom Carroll appears early in the film as a surfer with a cut eye. According to producer Brian Grazer, this is a real injury - Carroll had wiped out on the reef just seconds earlier - and it made the three cast members (Kate Bosworth, Michelle Rodriguez and Sanoe Lake) nervous about going in the water. The footage was shot for a surf video Carroll was part of and Grazer used it in the film, presumably because it added to the characters' anxiety at entering the surf and validated how dangerous it was.
Based on an article by Susan Orlean called "The Maui Surfer Girls" which was first published in 1998 in "Women Outside" magazine, and then in the book "The Bullfighter Checks Her Makeup" which is a collection of Orlean's profile articles.