The Smallville star plays Neried in the film, a feisty mermaid who falls in love with an Oxford-professor, played by her real-life fiance Billy Zane.
But while shooting one scene off the Greek island of Spetses, Brook sustained a minor head injury and struggled for air as her legs were strapped into her mermaid costume.
She says, "I held my breath as long as I could under water, then shot up and smacked my head on a huge Grecian column which was supposed to be part of a temple set.
"I suppose I panicked for a moment because my legs were trapped in the mermaid's fins and tail - the costume was stuck on and I was thrown into the sea with my legs strapped together.
"It was quite a bang on the head. I was dazed and saw stars and there was no way I could climb out on my own. Luckily some divers rescued me, but it was very painful and quite a shock."
British actress/model Kelly Brook knows exactly why people in the US are so fascinated by her natural assets.
The actress claimed that the reason behind why people admire her large natural breasts is not about the size, but because many people in Los Angeles have fake boobs so they like to watch her true ones.
"My breasts are a bit of a novelty in California," Hollywoodrag quoted Brooks, as telling FHM magazine.
Brook, whose recent modelling work for Triumph Bras caused quite a stir because of specially commissioned 50-foot high billboards of her bust, not just has her real breasts to be proud of but also her white teeth.
"And they go mad for my teeth as well. None of them can believe someone from England can have white teeth," she said.
The 'Smallville' star, who has a home in Hollywood which she shares with her fiancé actor Billy Zane, says that the two like spending time in the tinsletown, but prefer to spend much of their time at their home in the English countryside.
It seems when it comes to comparing U.S. and U.K., for Brooks everything from best food to best bust is available in U.K.
"We went to a barbecue at producer Lawrence Bender's place and everyone from Arnold Schwarzenegger to Sylvester Stallone was there. A Hollywood barbecue is nothing like an English one. There's no burnt burgers!," the actress said
