H2O: Just Add Water

Nakilala nina Cleo at Emma ang isang bagong babae, si Rikki, at natagpuan ang mga sarili nilang naipit sa Mako Island kung saan sila ay nag-anyong mga sirena. Kasama ng pagtubo ng mga buntot, nakita ng mga babae na may kapangyarihan sila sa tubig.

Annoying Miss Popularity, Miriam, is having a pool party and the girls want to go. But being around water is risky, especially when Zane tosses Cleo into the pool. Lewis is the only one around to help so he finds out their secret.

Rikki, Emma and Cleo discover that sea turtles are being captured by fishing nets. When Rikki and Emma attempt to rescue the turtles by cutting the nets, it causes the fisherman to think that there is a rogue shark roaming their ocean.

Emma decides that she is not going to have her annual sleepover party due to what has happened to them. But Rikki and Cleo try to convince her otherwise. Meanwhile, Lewis conducts experiments on the girls.

Cleo's sister Kim finds her diary and thinks that Cleo and her friends are 'evil mermaids' and she plans to tell everyone. Meanwhile, Lewis goes to Mako Island to find out more about what happened to the girls.

Rikki gains an admirer in Emma's younger brother Elliot when she saves him from drowning. She lets him down hard causing him to run away and hide in the fernery. The girls find him just as the watering system is about to start.

The effects of the full moon turns Emma into a carefree, wild mermaid. At her father's birthday party she's the opposite to her usual, organized self. Can the other girls stop her before all is revealed?

A charismatic newcomer, Dr. Denman, tempts Lewis with the promise of scientific fame and fortune. Will he abandon his friends and risk their secret, all in the name of science?

Rikki uses her abilities as a mermaid to earn some quick cash, but when she accidentally becomes involved in a fish smuggling operation, she sets out to get her revenge.

Rikki enters a short film contest on the theme of 'Heroes' and decides to capture some nice underwater footage with her 'abilities.' Meanwhile, Emma is interviewing her mom, and Zane and Lewis are planning to reenact Dr. Bennet's windsurfing record.

Byron asks Emma for help with training the school's swimming team and Emma has some trouble deciding whether or not to help out in her current situation. Meanwhile, Lewis continues to experiment on the girls, which annoys Rikki.

Rikki sets Cleo up at a karaoke contest as a joke, where she is humiliated due to her lack of talent. However, her singing ability undergoes a dramatic change when, in spite of the girls' precautions, she is hypnotized by the full moon.

When the mysterious, old Miss Chatham's boat and home is declared unseaworthy, Emma invites her to stay over. Zane gets trapped on the sinking boat and Emma tries to save him but he sees a tail.

Cleo's 16th birthday is approaching and she thinks that her father is going to throw another embarrassing birthday party. Meanwhile, Zane tries to find the 'sea monster' that he saw when he almost drowned.

Emma is put in charge of managing the juice bar. Miriam decides to cause trouble and cuts the power to the cool room, then is unwittingly frozen by Emma who uses her powers to fix the freezer. Will the girls be able to thaw Miriam out?

Ronnie, a new dolphin at the marine park, sees Cleo in the water and seems to fall in love with her, and Zane researches information at the park on the 'sea monster' he saw. A chain of events caused by these events leads to their family and friends thinking they're going out together.

A thunderstorm rolls in, leaving the girls little choice but to feign illness to avoid blowing their secret. However, their facade attracts far too much attention, and there might be only one solution for escape.

The full moon has come again, and the girls are taking every precaution they can imagine this time. It proves to be in vain, however, when Rikki falls under the spell.

Cleo and Kim are fighting like crazy and Cleo is pushed to her breaking point. Then cousin Angela comes to stay and things just get worse. Cleo realizes there are more challenging things than an annoying sister.

Lewis enters the annual fishing derby. When Cleo sees him struggling, she decides to help him out with disastrous consequences. Meanwhile, Rikki and Zane are trapped on a hotel balcony.

Zane thinks Miss Chatham holds the key to the sea monster. Emma needs a change so she dyes her hair red. While Zane gets closer to the secret, he also gets closer to Rikki. Zane dives to Miss Chatham's boat and sees a mermaid!

Emma and Cleo find out Zane and Rikki are an item and force her to choose him or them. When Zane appears to side with Harrison over the Mako Island development, Rikki's decision is clear. Now it's Zane's turn to make a choice.

The girls discover a necklace for sale identical to Miss Chatham's. Miriam causes a stir by buying it then throwing it in the water. Rikki faces a choice whether to take the necklace and reveal her mermaidness to Zane.

Lewis thinks he's found a way to control the girls' mermaidness. The school dance brings all our heroines' 'boy issues' to the surface.

It's time for Emma's family's annual vacation trip, but as it's too close to water, she can't risk it and her family isn't happy. This proves to be the least of the girls' worries, however: Dr. Denman has returned, and she stumbles upon one of Cleo's scales in the Moon Pool.