Colin Farrell and Alicja Bachleda dated while shooting the film, and had a son a year later. But they broke up in 2010.
When Ondine is wrapped in the Mylar blanket, the wind gives the appearance of her having a fish-tail.
The song played with the closing credits is Lisa Hannigan's "Braille." For some time the song was available for subscribers of Hannigans newsletter. An official release did not follow.
Stephen Rea plays a minor role in this film, and he also had a starring role in a similar "mermaid" film released in the same year, Nothing Personal (2009)
Annie runs her hand over a picture in a book. The book is Undine (about a water spirit who marries a knight to gain a soul) by Fredrich de la Motte Foque. The illustration Annie touches is by Arthur Rackham who was one of the leading figures of the golden age of British book illustration.