<Ul> <Li> Cariba Heine as Rikki, the new girl in town at the start of the show, who tends to be aloof and rebellious . Her power is the ability to control heat in water, ranging from warming to boiling, which eventually grows to allow her to control fire and lightning . Heine appears in all series of the show, and makes a special guest appearance in the spin - off series Mako: Island of Secrets . </Li> <Li> Claire Holt as Emma (series 1--2), who has a confident and responsible, if somewhat controlling, personality . She has the ability to freeze water, and later develops the ability to control clouds, ice and snow . Holt appears in series one and two, but left the show at the end of series two to film Messengers 2: The Scarecrow, with the character's departure explained as travelling the world with her family . </Li> <Li> Phoebe Tonkin as Cleo, who at first is shy and a little awkward and does not like water, but eventually becomes outgoing and personable . She is able to control and mould the form of water, as well as increase or decrease the amount of water present . She is later able to control the wind . Tonkin appears in all series of the show . </Li> <Li> Angus McLaren as Lewis, Cleo's childhood friend and later boyfriend who is academically gifted and thinks of himself as a scientist . He helps the girls keep their secret and works to understand how and why the girls transformed into mermaids . After appearing in both series one and two, McLaren left the show during the third series to begin filming Packed to the Rafters, but guest starred in the final episode of the show . </Li> <Li> Indiana Evans as Bella (series 3), the new girl in series three . She is a singer and performs at Rikki's cafe . Bella became a mermaid in the sea caves of Ireland when she was nine, and has the power to change water into gelatine and a crystalline substance . During the series, she and Will develop feelings for each other, and eventually become a couple . </Li> <Li> Luke Mitchell as Will (series 3), a skilled swimmer and free - diver who is introduced in series three . While exploring Mako Island, he finds the moon pool and is attacked by the water, causing him to search for the cause of the strange event . He is Bella's love interest and becomes closer to the girls once he discovers they are mermaids . </Li> </Ul> <Li> Cariba Heine as Rikki, the new girl in town at the start of the show, who tends to be aloof and rebellious . Her power is the ability to control heat in water, ranging from warming to boiling, which eventually grows to allow her to control fire and lightning . Heine appears in all series of the show, and makes a special guest appearance in the spin - off series Mako: Island of Secrets . </Li> <Li> Claire Holt as Emma (series 1--2), who has a confident and responsible, if somewhat controlling, personality . She has the ability to freeze water, and later develops the ability to control clouds, ice and snow . Holt appears in series one and two, but left the show at the end of series two to film Messengers 2: The Scarecrow, with the character's departure explained as travelling the world with her family . </Li> <Li> Phoebe Tonkin as Cleo, who at first is shy and a little awkward and does not like water, but eventually becomes outgoing and personable . She is able to control and mould the form of water, as well as increase or decrease the amount of water present . She is later able to control the wind . Tonkin appears in all series of the show . </Li>

When does h2o season 4 come out on netflix