Anna initially covered up with a pair of denim shorts and a black jacket, but soon stripped down to just her bathing suit.
She showed off her extremely lean frame as she filmed scenes for the upcoming movie.
The actress looked tense as she waded through the chilly sea.
(2005), Just Friends (2005), and My Super Ex-Girlfriend (2006).
The Just Friends actress was at one stage seen carrying a small girl on her shoulders as she waded through the waist-deep water.
She was also seen tightly embracing her 55-year-old co-star as they appeared to struggle to stay warm.
She received critical praise for her role in the indie black comedy Smiley Face (2007) and then starred in the Playboy-themed movie The House Bunny (2008), which was billed as her star vehicle and earned her an MTV Movie Award nomination for Best Comedic Performance.
' He's my longest boyfriend I've had for the last 16 years. When I was in the Spice Girls and doing my solo career, there just wasn't any time.