Emma wants to try something new and dies her hair red while in her mermaid form. Zane is on a trail to his "monster" which leads him back to sea to check the ship wreckage. There he saws Emma from the back exiting the wreckage but nobody believes him. Rikki agrees to go out with Zane but only if he stops with his obsession of wanting to prove that mermaid he was is the real thing.

Zane is determined to catch the "sea monster" he saw during his shipwreck, and he employs Lewis to help him. Lewis, even though looking for a part-time job, at first rejects his offer but after talking with the mermaids agrees to work with Zane to steer him off the Mako island. Cleo does not like her birthday party prepared for her as if she was still 6 years old, and goes for a long swim, but accidentally ends up where Zane and Lewis are.

Emma is helping a friend win a swimming competition while Lewis is doing all kinds of tests on Ricki and Cleo.

Cleo gets caught in the fishing net after trying to expose a poacher working for her dad who's using one of the boats to fish in the protected area of the sea where sea turtles are. Lewis calls the other two mermaids just in time to save Chloe and expose the poacher to her dad. Chloe is starting to accept who she is and what she can do underwater.

Girls are considering going to a pool party, but what with their problem with water and all, they decide not to go. But Cleo goes anyway and ends up being tossed inside the pool. Lewis comes to the rescue and find out she's a mermaid. Rikki discovers her new power of being able to make water evaporate or boil it.

Emma, Rikki and Cleo, three teenagers, found themselves marooned on an island after their boat runs out of fuel. The boat they took from a rich brat trying to pull a prank on Cleo. While on the island, they try to reach higher ground to get a cell phone signal, but Cleo falls down into a cavern. The two girls soon follow in a rescue attempt. They see a connecting pass through water as the only way out, but something magical happens as they all enter the water. Upon exiting on the other side, they get rescued by the harbor patrol. Next day, they find that upon touching the water they turn into mermaids. And not just that, but that they have the power to control the water itself.