H2O: Just Add Water Season 3 Episode 16 The Dark Side ( Air Date 2010-02-24 ) Genre Drama, Family, Sci-Fi & Fantasy category. Overview "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.".