The movie was shot in Australia with an Australian cast, but everyone uses an American accent, setting the movie in the US.
Of the cast only Nikita Ager (Venus) and Serah D'Laine (June) are American.
The mythological background for the mermaids in this movie is pulled from other stories and movies before it. The idea of mermaids not having an immortal soul (and needing a human to love them to have one), and turning into sea foam when they die is from Hans Christian Anderson. The idea of merfolk gaining legs when they step on land, but have a tail when in contact with water is from the movie Splash (1984). That movie also influences the sisters' ability to break glass with their high pitch voices. Lastly an Irish fable of a man who is able to keep a mermaid after he finds her red hat was used to create the background of the mermaids' birthright.
The idea of mermaids being bound to grant a wish to a human, literal or metaphorical, was created for this movie.
The mermaids are shown to have magical powers in this movie which was invented by the screen writers for the plot. Diana is shown to have super strength, Venus as a siren can hypnotize men, and June can communicate with sea animals. Venus is also shown to be able to telekinetically move a treasure chest under water, but it is not clear if this is a power that is only hers or that the others have as well.