• Beauty, Brains, and Brawn: With sweet and shy Cleo as Beauty, smart and responsible Emma as Brains, and tomboyish Rikki as Brawn. When Emma leaves in season 3, Cleo eventually went into Brains territory while Dude Magnet Bella took over the Beauty spot.
• Blessed with Suck: For our heroines, contact with water is not always a pleasant thing. Given how much water exists in day-to-day life, the girls are always a hair's breadth from being discovered as mermaids.
• Childhood Friends: Emma and Cleo are childhood friends, and both meet new girl Rikki in the first episode. Bella is the new friend when Emma leaves in season 3.
• Fanservice Pack: Season 2 has the girls wearing a lot more figure flattering clothing and sexier outfits, especially for Cleo. Many fans experienced She's All Grown Up feelings.
• Making a Splash: All of them have varying powers and abilities over water.
• Freudian Trio:
  • Seasons 1 and 2
    • Id: Rikki — Crass, insensitive, quickest to suggest using powers for amusement.
    • Superego: Emma — Responsible, refined, always has a plan for anything.
    • Ego: Cleo — Middle of the road, always bridging the gap between the above pair.
  • Season 3
    • Superego: Rikki — Runs her cafe, maintains that their secret is more important than what they want.
    • Id: Bella — Easily swayed by her crush on Will and lets her heart get her into trouble.
    • Ego: Cleo — Still middle of the road trying to keep the other two on speaking terms.
• Nice Mean And In Between: Meek but kind Cleo as Nice, hot-tempered Deadpan Snarker Rikki as Mean, and bossy yet well-meaning Emma as In-Between. Occasionally Rikki and Emma will swap around, with Emma getting so bossy that she is condescending, and Rikki proving to be a Jerk with a Heart of Gold. Bella in season 3 is another In-Between.
• Organic Bra: In their mermaid forms, all the girls have their chest covered by scales the same colour as their tails, in the shape of a bikini top.
• Our Mermaids Are Different: After finding their way to a mysterious island, they turn into mermaids following "The Splash Method" after swimming in a Magical Pool during a full moon. They also have powers over water: one can freeze it at will, one can boil it at will, and the other controls it at will (also she can multiply it from a drop to a bucket). Congruent with their origin, the full moon can have weird effects on them if they see it (what effects depends on planetary alignments), and in one case, permanently increase their powers.
• Super Not-Drowning Skills: Being mermaids, they can stay underwater longer than humans. They can't breathe or speak underwater (a natural limitation of being played by human actresses), but in their first few days of being mermaids, they find that they can hold their breath for fifteen minutes with no trouble, and only grow stronger with experience.
• Town Girls:
  • The first two seasons have sweet naive Cleo (femme), level-headed Emma (neither) and rebellious tomboy Rikki (butch).
  • In season 3, Rikki is still the butch, Idol Singer Dude Magnet Bella takes over the femme role, and Cleo becomes the neither.
• Water-Triggered Change: The girls change from human to mermaid upon coming into contact with water, no matter the amount. They revert back to human once they're dried off.

Cleo Sertori

^{Click here for her mermaid form}

• Ambiguously Brown: Has a bit of a deeper complexion that none of the rest of her family have.
• Animal Lover: While she can be shy and awkward around people, Cleo has a deep love for animals, shown in how lovingly she takes care of her fish tank and of the dolphins at her theme park job, as well as her rescue of a pelican and several turtles.
• Betty and Veronica: The Betty to Charlotte's Veronica and Lewis' Archie, having known Lewis for nearly all their lives, being shy and usually sweet and not very forward about her feelings.
• Blow You Away: Season 2 has her powers increase, giving her the ability to manipulate the wind.
• Can't Spit It Out: Her feelings for Lewis are plain on sight for everyone throughout Season 1, and after they've broken up in Season 2, it's again obvious that she isn't over him, but she can't get herself to just tell him that for the longest time.
• Clingy Jealous Girl: In early Season 2, 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...while insisting to Charlotte that she and Lewis are Just Friends.
• Cool Big Sis: She may get into arguments with Kim, but she loves her regardless. After their parents' divorce, they start getting along better.
• Defrosting Ice Queen: Downplayed, but toward Charlotte. Cleo starts Season 2 very jealous of her and eager to push her away, but time has her mellow out and accepting Lewis' relationship with Charlotte, and when the latter becomes a mermaid, Cleo is ready to include her in their friend group and help her along regarding magical things.
• Heel Realization: After her initially very poor reaction to Charlotte taking an interest in Lewis, she notes that she was the one who ended the relationship to the latter, and tries to be more of an adult about the former.
• Ironic Fear: Initially struggles with a fear of water.
• Making a Splash: Her powers involve shaping water.
• Naïve Everygirl: The most naive and insecure of the main girls.
• The Scapegoat: She has to take a lot of blame over the course of Season 2, usually from Charlotte, when it's mostly Emma and Rikki who are up to shenanigans.
  • Similarly, Charlotte blames her for still being close to Lewis, but it's actually Lewis who more often than not still seeks out Cleo's company when Cleo tries to put up boundaries after their break-up.
• 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.
• Sickeningly Sweethearts: With Lewis, according to Rikki.

Emma Gilbert

^{Click here for her mermaid form}

• An Ice Person: Her water-powers involve frozen water particularly.
• The Ace: Fits this description the most of all the main cast.
• Blue Blood: Downplayed; she comes from a family of white collar workers.
• 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 (e.g., 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 dialogue about it and try to negotiate and compromise, Emma just tried to sabotage him to get him fired.
• Cool Big Sis: Her little brother Elliot has absolute trust in her and looks up to her.
• 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 usually cause her to get sucked into the wackiness too.
• Put on a Bus: In Season 3.
• Socialite: She lives in high society unlike the other girls.
• The Smart Girl: Probably the smartest of the three mermaids. Also often "smart" as in sensible.
• Spoiled Sweet: She is upper class, but not as bad as the other white collar characters in the show.
• Tsundere: For Ash. She initially hates his guts because he breaks up her routine at the Juicenet café with smiling confidence, 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

^{Click here for her mermaid form}

• Back for the Finale: An adult Rikki provides the only Required Spinoff Crossover in the two-part finale of daughter show Mako Mermaids: An H₂O Adventure, where she's become a renowned maritime salvager by secretly using her mermaid powers. She's surprised to discover the Mako Mermaids protagonists are real mermaids, as that's very much outside context for her home series, and resolves to try to get back in touch with her friends.
• Boring, but Practical: One of the most frequent uses of her heat based powers is to evaporate any water touching her or her friends to quickly undo the mermaid transformation or to stop it from happening in the first place.
• Burning with Anger: She has anger issues and fire powers. Especially highlighted in her full moon episode, when her inability to control her powers is a metaphor for her inability to control her emotions.
• 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.
• Friendless Background: Starts out with no friends, due to being new in town.
• Hidden Depths: In Season 1, she not only participates in an investment seminar on her own cost, she also sees right through the fraudulent nature of the advertised straregies, hinting that she might dream of a financially more successful future — and is very well sharp enough to achieve it.
• 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.
• Nice Job Breaking It, Hero: Charlotte might not have gone over the edge if Rikki hadn't been so hostile to her. While Cleo got most of the blame for it, it's usually Rikki who insists on trying to make Charlotte look bad, attempts a Relationship Sabotage, and wants to exclude her from the circle of mermaids.
• 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.
• Shock and Awe: Her new powers as of Season 2 involve lightning bolts. Needless to say, it's a bad combination with her explosive temper.
• Slap-Slap-Kiss: Her relationship with Zane.
  • Foil: Even though Zane is wealthy and Rikki is poor, they both have dysfunctional home lives. (This is not a Dysfunction Junction show, and Emma and Cleo have good families, and thus Rikki's friends don't understand that aspect of her life.)
• Sociopathic Hero: Admittedly, she was under the influence of the full moon at the time, but her nearly hitting Charlotte with lightning was still motivated by Rikki's dislike for her.
• Tomboy: She is easily the tomboy of the group (for looks, attitude, background, etc). Even Passionate Sports Girl Emma is far girlier than Rikki.
• Tsundere: To Zane.

Isabella "Bella" Hartley

^{Click here for her mermaid form}

• Dude Magnet: Lampshaded when Rikki tells Bella that she only likes Will because "he's the only guy in a five-mile radius not to swoon over [her]".
• Everyone Loves Blondes
• Genki Girl: Bella is described as being a bubbly ball of energy who's easy to talk to.
• Idol Singer: She is a singer and performs at Rikki's cafe.
• Sixth Ranger: Joins Cleo and Rikki after Emma leaves.
• Stuff Blowing Up: One of her powers.
• Suspiciously Similar Substitute: To Emma.
• Transmutation: Bella's power changes the physics of water, allowing her to turn it to jelly or glass.

Lewis McCartney

• Absent-Minded Professor: He can get a bit wrapped up in his experiments and studies. It cost him the chance to ask Cleo to the school dance, and also plays a part in their relationship going awry as Lewis fixates on trying to figure out the girls' magical powers instead of giving Cleo the sort of emotional support she needs.
• Back for the Finale: Written out halfway through Season 3, he manages to come visit Cleo in the final moments of the series finale.
• Betty and Veronica: The Archie to Cleo's Betty and Charlotte's Veronica.
• Childhood Friend Romance: He and Cleo have known each other since their ages were in the single digits, and they're clearly in love with each other in the present day.
• Didn't Think This Through: He's very smart altogether, but specific situations can have him be a bit short-sighted.
  • Following three mermaids out to Mako Island at night when he knows from experience that they're out of control under the full moon leaves him rattled by their new powers.
  • Splashing Charlotte with water in a public place to see if she grows a fishtail? Really?
  • Cleo points out that it wasn't a great idea to introduce Charlotte to Ronnie in an attempt to have her overcome her fear of dolphins; Cleo knows how to handle Ronnie and that he can be a tad too playful to seem harmless, but neither Lewis nor Charlotte do.
• Distressed Dude: Several times. In Season 1, he's kidnapped by Dr. Denman's assistants and held hostage against the girls' compliance; Zane has to help him break out. Come Season 2, he's at first at the mercy of three moon-crazed mermaids who use their new superpowers on him, later on at that of his also super-powered girlfriend when she lashes out with jealousy.
• Dude, Not Funny!: He calls Charlotte out on scaring and later on bullying Cleo, both of which she recounts with a proud grin.
• Extreme Doormat: A mild case towards the girls; especially Rikki can be rather bossy with him. It's way more pronounced in his relationship with Charlotte — even his getting together with her in the first place was more of a case of Lewis being unable to openly say no, and she quickly gets into the habit of ordering him around.
• Flat-Earth Atheist: Downplayed. While he is somewhat open to the mermaids' powers being magical in nature, it doesn't stop him from trying to find scientific explanations and solutions to their problems, e.g. he is right about different lunar alignments having different effects on them, but he cannot figure out what the effects will be or why.
• It's All About Me: Not usually, but after Cleo has broken up with him, he tends to jump to conclusions that every other thing she says or does is about him, and her wanting him back — had he taken the time to listen to her concerns, he'd know that she was still gnawing on her parents' divorce, and wasn't trying to Relationship Sabotage him and Charlotte but her own father and Charlotte's mother. It's making it harder for Cleo to try and cope with the situation like a responsible adult.
• Knight of Cerebus: An inversion. The cast's relationships begin to deteriorate, and the plot becomes much more serious, after he leaves.
• The Masquerade Will Kill Your Dating Life: Experiences this a lot in his relationship with Charlotte, due to having to assist the girls in their problems.
• 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, especially from Rikki's point of view. It's also the reason why he and Cleo break up; he just cannot stop hovering...though he doesn't really after their break-up, either. To the girls' utter annoyance, that means Charlotte will trail after him as he's trailing after them.

Will Benjamin

• 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.
• Loving a Shadow: He admits that his attraction to Bella is because of what she is (a mermaid), not who she is.
• Secret Chaser: Encountering the water tentacle in the Moon Pool causes him to become curious about the pool, and the girls who came to his rescue. He eventually notices that Bella flees from water, and manages to force her secret out of her by splashing her when she can't easily run away from him.

Dr. Linda Denman

• Beauty Is Bad: A strikingly beautiful woman, and she kidnaps four teenagers and threatens them with bodily harm for her own profit.
• Big Bad: Of Season 1.
• Head-Turning Beauty: Lewis lampshades that she looks more like a model than a scientist.
• Karma Houdini: Let's recount Dr. Denman's crimes: Four counts of kidnapping, with the intent of forcibly experimenting on three people, and threatening Lewis' life to keep the girls in line. No legal trouble, no harm done to her career, nothing. No one other than a few people ever find out, so not even her reputation suffers. She just...doesn't get to do the experiments she wanted.
  • To be fair, they couldn't exactly have her arrested without explaining why she would kidnap them.
• Obliviously Evil: Somehow, she doesn't seem to grasp at all that kidnapping minors, holding them prisoner and away from their families and planning to use them as guinea pigs is both highly unethical and criminal. When the girls can't help themselves in any other way than fighting her off via their powers and finally by giving said powers up, Denman doesn't appear to grasp that she is the one who created this situation for them.
  Dr. Denman: Why would you give up being mermaids?
  Cleo: Because of people like you.
• Secret Chaser: Lewis leaves one of Cleo's scales in her lab, which she studies and realizes the creature it came from has human DNA. She spends the rest of the season searching for the creature's whereabouts, and succeeds thanks to Zane's mermaid hunt.

Charlotte Watsford

^{Click here for her mermaid form}

• All Your Powers Combined: Has the powers of Emma, Cleo and Rikki all in one, as she went into the pool on her own at the full moon where the three girls were in the pool together.
• Betty and Veronica: The Veronica to Cleo's Betty, the confident, artistically interested new girl who openly flirts with Lewis and has a bit of an edge to her attitude.
• Big Bad: Of Season 2.
• Bitch in Sheep's Clothing: Subtle for the most part of the season, but she is spiteful to Cleo as soon as their rivalry over Lewis becomes clear; this includes intentionally making Cleo look bad in front of her family or Lewis, rummaging through her things without permission ^note and making a move like she wants to steal Cleo's necklace, and ever again intentionally rubbing in that she's spending time with Lewis — all with a sugary sweet smile on her face.
  • Less subtly, her relationship with Lewis has abusive traits, such as her following him everywhere (including when he's at the house of one of the girls), declining phone calls for him without his knowledge, bossing him around and guilt-tripping him when he wants to spend time with anyone but her.
• Blonde, Brunette, Redhead: The redhead to Cleo's brunette and Rikki and Emma's blondes.
• Blue Blood: Her mother owns a restaurant, and judging by the house they live in and the party she organizes for Lewis' birthday, she seems to move in somewhat high society.
• Brought Down to Normal: Has her powers permanently stripped from her after trying to strip the girls of their 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. Although, this could be because they no longer consider her a threat now that she's permanently human, and even if she tried to tell anyone, everyone would think she's crazy.
• Entitled Bitch: Lewis aside, Charlotte thinks she is owed mermaidhood simply because her grandmother was one, she is owed Gracie's necklace (that she literally forcibly rips from Cleo's neck), and that the girls should fall all over themselves to involve her in their "secret club"...when the first thing she does to introduce them to the idea is scaring Cleo and laughing about it, and then turning down all their advice.
• Entitled to Have You: Starts showing this attitude about Lewis, pushing him to ask her out for no better reason than she wants it. After he breaks up with her, she loses touch with reality, insisting that he wants her back.
• Evil Cannot Comprehend Good: Is utterly flabbergasted why Lewis would dump her on the spot for a "weak" mermaid like Cleo. She doesn't seem to understand that Lewis prefers Cleo because of how genuine their love is, and he dumped Charlotte because of how toxic and controlling she is.
• Evil Eyebrows: To give her a more sinister expression, Brittany Byrnes' natural eyebrows have been elongated and plucked to thinner, high arcs. It helps emphasize Charlotte's onsetting ruthlessness.
• Evil Redhead: She's pleasant enough for most of the season, but after becoming a mermaid her powers completely go to her head and she takes out her frustration against the girls quite cruelly, especially Cleo, trying to deliberately keep them and Lewis apart, and, later, trying to strip them of their powers permanently.
• Face–Heel Turn: Charlotte's mermaid powers apparently go straight to her head. After losing them, she becomes nicer.
• Graceful Loser: She accepts her powers are gone and gives up on trying to make Lewis her boyfriend.
• Green-Eyed Monster: Cleo started out as one to her, but once Charlotte is in a relationship with Lewis, the tide turns, and she resorts to massively bullying Cleo and telling her how worthless she is and all the things she doesn't deserve.
• Heel–Face Turn: Once Brought Down to Normal.
• Idiot Ball: There is zero explanation for why Charlotte jumped into Ronnie the dolphin's tank when he splashed her and she was transforming. The previous episode has her learning how to dry herself off with her powers quickly, and there's no one around to see her, so the situation of her getting into a panic over the proximity of a dolphin seems rather contrived.
• I Just Want to Be Special: Believes that since her grandmother was a mermaid, it's her destiny to become one as well, and believes that it would make Lewis give her the same attention he gives Cleo.
• 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 for no reason, despite the fact she locked Cleo and Emma in a pool room with a leaky pipe, which she intentionally sabotaged trapping them - with dozens of unsuspecting people around!
• Karma Houdini: Charlotte is stripped of her mermaid powers, which is arguably less of a punishment than what is needed to do to stop her hazardous power trip. Beyond that, she never gets any comeuppance for stalking and controlling Lewis, lying to everyone around including her own mother and the girls' families, breaking and entering, attacking Emma's house, stealing from Cleo's things, and bullying Cleo almost to the point of suicide.
• Love at First Sight: One of the early signs of her obsessive tendencies is her getting heart eyes at Lewis before he has even said a word to her.
• Manipulative Bitch: Her earlier barbs go largely unnoticed, but she tries as early as of the sixth episode of Season 2 to make Cleo look bad, pouring flour over her and laughing about it, and then goes on to repeatedly rub her blooming relationship with Lewis in Cleo's face, knowing that the latter is hurting about it. She's also not above pushing in as Cleo's tutor to make sure Lewis doesn't spend any time with Cleo tutoring her, and repeatedly implies to him that Cleo doesn't want to see him in an attempt to drive a wedge into their persisting friendship.
• 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.
  • She pushes in on the Sertori's family trip when she learns that not only Rikki and Emma, but also Lewis will come along...then complains that Cleo is around.
  • As a mermaid, she complains about being babied by the girls...except that she is extremely careless with her powers, around water and their shared status as mermaids in public, proving that she has no sense of responsibility over their secret. She even submits willingly to the erratic power of the full moon.
  • She sneaks into Ronnie the dolphin's tank without permission or guidance, plays with him and even jumps into the water to him when she's accidentally transformed, then panics at Ronnie trying to interact and attacks him. It was her idea to be there in the first place, and to get into closer proximity to an animal she knows she's afraid of.
• No Accounting for Taste: Considering how much time she spends mad at Lewis, distrustful of Lewis, and criticizing Lewis, you have to wonder why she's even so eager to be with him in the first place.
• Oh, Crap!: After the trio use their advanced powers to destroy her water snakes. Then when they overpower her and hover her over the Moon Pool, that's when she realizes that she's the weak mermaid.
• Playing the Victim Card: For someone who feels so unfairly treated by the girls and sidelined by Cleo's persisting friendship with Lewis, she seems to take a lot of glee in bullying Cleo whenever the opportunity arises^note  like taunting her for a presumed fear of water, and she monopolises Lewis to the point where she forcibly prevents his contact to Cleo and the others. It's also a bit rich of her to accuse Cleo of constantly being around for a Relationship Sabotage on her and Lewis while she literally seeks out Cleo several times just to rub her latest date with Lewis in the latter's face.
• Screw the Rules, I Have Supernatural Powers!: Eventually tilts over into this; she thinks having more magical gifts than the other girls gives her perfect validation to recklessly use them in public, and against people she doesn't like; she nearly kills Nate in a fit of rage, and then attacks the girls.
• Smug Smiler: Everytime she gets to either make Cleo look bad or mock her, such as scaring Cleo when Charlotte suddenly showed up as a mermaid.
• Smug Super: As soon as she starts learning her powers, she uses them to mess with the other girls in petty ways. When it turns out she has all three of Cleo, Emma, and Rikki's powers, she starts calling herself a "super mermaid".
• Statuesque Stunner: A very pretty girl who's, at 5'8", notably taller than her boyfriend.
• Took a Level in Jerkass: She was decent person in the beginning, but got worse when she started pursuing Lewis, and worse still 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.
  • Admittedly, she didn't start out great in the first place — her methods of wooing Lewis include stalking him everywhere he goes and pretending to like the same things he likes to get to spend time with him, even when she doesn't care about his interests.

Sophie Benjamin

• Big Bad: Of Season 3.
• 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.
• Took a Level in Kindness: When Mako Island undergoes an avalanche, her brother Will asks her which means more to her - either him or the money. She then takes Will's side and escapes. At the school graduation, she presumably apologizes to the girls and becomes on better terms with him and her brother.

• Heel Realization: When Dr. Denman has caught the mermaids with Zane's and Mr. Bennett's help, Zane's triumph over having his mermaid theory proven only lasts moments as he finds his girlfriend and her friends imprisoned, and quickly turns against the ruthless scientists.
• Hidden Depths: Season 2 reveals that he takes an interest in motorcycles, both for sports and the mechanical aspects.
• 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.
• Secret Chaser: He glimpses Emma's mermaid form in "Shipwrecked" and spends a good deal of time afterwards trying to find the supposed sea monster.
• Secret-Keeper: Becomes this by the end of Season 1.
• Slap-Slap-Kiss: He has this relationship with Rikki.
• Took a Level in Jerkass: In Season 3, he cheats on Rikki with Sophie, proves to be a terrible boss at the café in every sense, and ends up helping Ryan try to mine the moonstones out of the Moon Pool for money. Rikki ends up dumping him, and they never get back together.

• Chuck Cunningham Syndrome: Disappeared after Season 1 with no explanation.
• Mellow Fellow
• Nice Guy

• Alpha Bitch: Miriam is the school's rich, popular girl, and not a nice person.
• Chuck Cunningham Syndrome: Also disappeared after season 1 with no explanation.

• Beta Bitch: She's almost as mean as Miriam.
• Chuck Cunningham Syndrome: Disappears after season 1.
• Hopeless Suitor: She has a crush on Lewis, who is blatantly in love with Cleo.
• Token Minority: Is one of the few minorities we see during the show.

• Ambiguous Situation: She claims to have given up being a mermaid, though subsequent material would later show that it's actually extremely difficult to break the enchantment, and only Gracie was confirmed to have used the fifty-year full moon on herself. On top of that, she still seems to have supernatural abilities, yet she's never seen getting wet in the present day, leaving it unknown if she still has her powers or not.
• Cloudcuckoolander: She appears to be one of these.
• Cool Old Lady: Turns out to be one of these.
• Eccentric Mentor: She's trying to mentor the girls the way she and her friends weren't. Her habit of being cryptic and disappearing when no one is looking at her tend to frustrate them instead, especially Rikki.

• I Just Want to Be Normal: Gave up her powers as she missed being an ordinary girl with no major secrets to keep.

• Out of Focus: Out of the three original mermaids no much is known about her later life seeing as she died offscreen in Season 1 which lead to Rikki inheriting her locket.

• Did Not Get the Girl: Gracie was convinced that he loved the mermaid half of her more, and broke up with him while giving up her powers.
• The Smart Guy: He was the Lewis analogue for the previous generation, and has finding about Mako Island that he refuses to share with the world.