H2O: Just Add Water - Season 3 - Eps 16: The Dark Side
Rikki's frustrated by the water attacks and goes to Mako Island on a full moon to confront the strange force in the Moon Pool. With Cleo and Bella delayed, Will pursues her and discovers she's been affected by the experience.
About H2O: Just Add Water

Title: H2O: Just Add Water
First Air Date: 2006-07-07
Last Air Date: 2010-04-16
Status: Ended
Rating: 7.812/10 (from 653 votes)
Language: EN
Seasons: 3
Total Episodes: 78
Network: Network Ten
Genres: Drama, Family, Sci-Fi & Fantasy
Production Companies: Pacific Film and Television Commission, Jonathan M. Shiff Productions, Network Ten, ZDF
Synopsis
H2O: Just Add Water revolves around three teenage girls facing everyday teen problems with an added twist: they cope with the burden of growing a giant fin and transforming into mermaids whenever they come in contact with water.
Cast

Phoebe Tonkin
Cleo Sertori

Cariba Heine
Rikki Chadwick

Indiana Evans
Isabel "Bella" Hartley

Luke Mitchell
Will Benjamin

Burgess Abernethy
Zane Bennett