The girls' powers are as follows: Cleo can manipulate water, Emma can freeze water, and Rikki can boil water. In season 2, they gained weather control: Cleo can manipulate wind, Emma can draw moisture from the air to freeze, and Rikki can draw forth lightning which catches things on fire. Bella, the mermaid introduced in season 3, can crystallize and gelatinize water.
The role of Charlotte Watsford was nearly awarded to actress Gemma Forsyth before Brittany Byrnes was officially cast. Forsyth went on to portray Evie McLaren in the show's spin-off series Mako Mermaids (2013).
Only two seasons with a total of 52 episodes were originally planned but, due to popular demand, a third and final season was filmed. Season one premiered in July 2006, followed by season two in September 2007. Season three first aired in the United Kingdom in October 2009, with the Australian premiere occurring in May 2010.
It first screened on Australia's Network Ten and runs in syndication on channels in over 120 countries and has a worldwide audience of more than 250 million. It was filmed on location at Sea World and other locations on the Gold Coast.
The theme song at the beginning of each episode is sang by a different singer each season. Season 1 was Ellie Henderson, season 2 was Kate Alexa, and season 3 was Indiana Evans who also portrayed Isabella Hartley.
During preproduction, each girl that would be a mermaid during the season would get a molding done of her legs so they could make the mermaid tails for the scenes where they are in mermaid form. Before they were able to swim with the tails on, they had to go through a rigorous training process to get their bodies ready for the extra weight of the tails. They also learned breath holding exercises to help them with holding their breath underwater for long periods of time.