Cleo Setori, Mermaid of Waves
Cleo Sertori (Phoebe Tonkin) is the brunette of the group and a bit awkward, but eventually becomes more outgoing. Her powers are manipulating the shape of water, including the ability to create more water out of an existing amount. She later gains the Razor Wind power.
- Clingy Jealous Girl: In season two, Cleo breaks it off with Lewis, stating that she can't have a boyfriend. Then when Charlotte comes along, she gets jealous and angry whenever they hang out and do things, even at one point sabotaging a dinner to try and drive the two apart. Meanwhile, Charlotte's only real "crime" is trying to make advances on an apparently single guy, as Cleo insists to her that they're "just friends."
- Cool Big Sis: She may get into arguments with Kim, but she loves her regardless.
- Making a Splash: her powers involve shaping water
- Naïve Everygirl: The most naive and insecure of the main girls.
- Nice Job Breaking It, Hero!: Charlotte probably wouldn't have gone over the edge if Cleo hadn't been so hostile to her.
- Shrinking Violet: Unlike her more confident friends Rikki and Emma, Cleo tends to be quite shy.
- Sibling Rivalry: With her younger sister, Kim. They share very heartwarming moments on a good day.
Emma Gilbert, Mermaid of Ice
Emma Gilbert (Claire Holt), the "leader" of the group, is a rather serious and responsible girl. She has powers to freeze water and manipulate ice, snow, and clouds. Her actress is noticeably missing from the third series; she left to film a straight-to-video prequel to The Messengers.
- An Ice Person: Her water-powers involve frozen water particularly.
- Control Freak: A pretty good example of this is when Juicenet got a new manager who started making changes around the cafe, some of which were pretty sensible (EG, removing a product from the menu that wasn't selling, and rearranging the cold room so that the fresh fruit wouldn't freeze and thus lose flavor). Rather than try to open a dialog about it and try to negotiate and compromise, Emma just tried to sabotage him to get him fired.
- Defrosting Ice Queen: She's incredibly uptight early on in the series, but does mellow out.
- Gag Haircut: She decides to colour her hair. Unfortunately she picks something called 'Scarlet Fever'. The results are disastrous, but thankfully it's only in mermaid form.
- Not So Above It All: She gets a lot of moments like this, usually provoked by Rikki.
- Only Sane Woman: In the main trio. She tries to be anyway, but her neurotic tendencies can usually cause her to get sucked into the wackiness too.
- Put on a Bus: in season 3.
- The Smart Girl: Probably the smartest of the three mermaids. Also often "smart" as in sensible.
- Tsundere: For Ash. She initially hated his guts for some reason, but she eventually falls for him.
- "Walk on the Wild Side" Episode: When her parents are away, she decides to throw a Wild Teen Party. To a lesser extent, she gets tired of being known as dependable and colours her hair.
Rikki Chadwick, Mermaid of Fire
Rikki Chadwick (Cariba Heine) is the "Wild Child" of the group. She is the new girl in town but not a Naïve Newcomer, because she is rebellious and confident. Her powers initially involve manipulating heat in water (i.e. boiling it), but eventually extend to control over fire and lightning.
- Deadpan Snarker: In one interview Cariba Heine said that Rikki's dry one liners was the thing she liked the most about her character.
- Establishing Character Moment: Her first scene in the first episode has her jump into a boat from the dock to help Cleo after Cleo gets set adrift by Zane. She then reveals that she stole the sparkplug from Zane's because she doesn't like him. This establishes her as a fearless rebel with a dislike of Jerk Jock types and little regard for personal property, but still a basically decent person at heart.
- Jerk with a Heart of Gold: Rebellious, blunt, and sarcastic but ultimately a good person.
- Missing Mom: Her parents are divorced and she lives with her father.
- Playing with Fire: her powers of temperature manipulation evolve into this over time
- Relationship Sabotage: Instigates and helps Emma and Cleo to do this to Lewis and Charlotte.
- Slap-Slap-Kiss: Her relationship with Zane.
- Tomboy: She is easily the tomboy of the group (for looks, attitude, backgroud, etc). Even Passionate Sports Girl Emma is far girlier than Rikki.
- Tsundere: To Zane.
A mermaid since the age of nine, Bella moves to Mako Island from Ireland in Season 3. Her powers are turning water into gelatine, making water harden into crystal, and to densely compact particles to make substances explode.
- Genki Girl: Bella is described as being a bubbly ball of energy.
- Idol Singer: She is a singer and performs at Rikki's cafe.
- Making a Splash: Her magic gives her some specific powers over water
- Sixth Ranger: Joins Cleo and Rikki after Emma leaves.
- Stuff Blowing Up: One of her powers.
- Suspiciously Similar Substitute: To Emma.
- Knight of Cerebus: An inversion. The cast's relationships begin to deteriorate, and the plot becomes much more serious, after he leaves.
- Nice Guy: He's always willing to help out others when they are in need of assistance as well as being reliable and can always keep a secret no matter what.
- Secret Keeper: He helps the girls keep their secret.
- The Smart Guy: He is academically gifted, likes to think of himself as a scientist and enjoys building many types of inventions such as weather analyses and recycling units.
- Unwanted Assistance: In-universe. This is the reason why he and Cleo broke up.
- Jerk with a Heart of Gold: Starts out as an arrogant and bullying bad boy, but he really falls in love with Rikki and eventually shows his nice and caring side.
- Lonely Rich Kid: He's very rich and has a complicated relationship with his father.
- Slap-Slap-Kiss: has this relationship with Rikki.
- Your Cheating Heart: In the third season, his relationship with Rikki was strained - and in the heat of a happy moment, he and Sophie shared a kiss, though it apparently never went anywhere.
- Big Bad: Of Season 1.
- Hot Scientist: Lewis lampshades that she looks more like a model than a scientist.
- Cloudcuckoolander: She appears to be one of these.
- Chuck Cunningham Syndrome: Disappeared after Season 1 with no explanation.
- Alpha Bitch: Miriam is not a nice person.
- Brother Chuck: Also disappeared after season 1 with no explanation.
- Big Bad: Of Season 2.
- Blonde, Brunette, Redhead: The redhead to Cleo's brunette and Rikki and Emma's blondes.
- Brought Down to Normal: Has her powers permanently stripped from her after trying to strip Cleo, Emma, and Rikki's powers.
- Easily Forgiven: The girls seem to get over the fact that she spent almost an entire season hating their guts and trying to hurt them whenever possible rather quickly.
- Evil Redhead: She's pleasant enough for most of the season, but after becoming a mermaid her powers apparently go to her head and she takes out her (not unjustified) frustrations against the girls quite cruelly, even trying to deliberately keep them and Lewis apart, and later, trying to strip them of their powers permanently.
- FaceHeel Turn: Charlotte's mermaid powers apparently go straight to her head. After losing them, she became nicer.
- Graceful Loser: She accepts her powers are gone and gives up on trying to make Lewis her boyfriend.
- HeelFace Turn: Once Brought Down to Normal.
- It's All About Me: Her idea for Lewis's birthday party was a surprise party with all the guests being people she knows. Plus, she thinks that the girls cut ties with her was for no reason, despite the fact she locked Cleo and Emma in a pool room with a leaky pipe.
- Never My Fault: Blames the girls, namely Cleo, for her relationship with Lewis getting ruined. It's because she's rude, controlling and vindictive to anyone who interferes with her plans.
- Took a Level in Jerkass: She was decent person in the begining, but got worse after getting her mermaid powers.
- Unwitting Muggle Friend: To Lewis. Lewis constantly lying to her or giving her evasive answers and standing her up and inevitably ending up around Cleo (who says that they're "just friends," but acts like a Clingy Jealous Girl regardless) is the reason she starts getting suspicious of him and the girls.
- Yandere: She slowly turns into this for Lewis. Her goal for the season finale is to get rid of the girls' powers so that she'd be the only mermaid.
- I Just Want to Be Normal: Shades of this, as we find out that he isn't so interested in being a world-class competition diver.
- Big Bad: Of season three.
- Big Sister Instinct: She pushes her brother Will to excel in diving, believing she has his bests interests at heart.
- Clingy Jealous Girl: ...But this is what she comes off more as.
- Evil Redhead: She wants to support herself and her brother, but her greed becomes her downfall.
- Greed: Her fatal flaw.
- Manipulative Bitch: She uses Zane and Rikki to get the manager position and tries to control her brother's relationship with Bella.
- Relationship Sabotage: Her flirting with Zane eventually destroys Zane and Rikki's relationship.