Alternate Character Interpretation: With The Reveal in Season 2 that Rikki is actually a lonely poor kid, her dislike of Zane in Season 1 has multiple possibilities. The first is that she just thinks he's a jerk. The second is that she hates him because she's jealous of what she doesn't have. The third is that there could be romantic feelings from the start but she's acting Tsundere because she believes he'd never be interested in a poor girl.
Angst? What Angst?: Cleo and Kim's parents divorce offscreen between season one and two. It's briefly mentioned, and neither the girls nor their father show any emotional turmoil at all. What's more is that while a couple of episodes do address it, it's entirely from Cleo's perspective. Kim doesn't seem bothered at all by the fact that her mother just up and left. Their father doesn't seem to be affected by losing his wife at all. And the mother is never seen again, yet the issue is glossed over.
Emma. She's either a well-meaning girl with a few neurotic tendencies or a bossy and controlling harpy who tries to lecture her friends every chance she gets.
This also affects Bella, depending on the attitude to Emma. Either she was a Replacement Scrappy or a massive improvement.
Character Derailment: Zane in season 3, big time. He basically goes back to being snobby, scammy, stubborn jerk, even going as far as kissing Will's "evil" sister, Sophie, right in front of Rikki, his GIRLFRIEND, and then declaring "it was nothing" to Rikki, when she rightfully called him out on it. Later, he tries to blackmail her into coming back to him, while Sophie is still close. It's like he was stripped off his previous character development, where he could be mean, pushy, but not as horrible as there.
Also, Charlotte who started as a really nice and sweet person. She wasn't even pushy in the beginning, being ok with Lewis turning her down from time to time and just being friendly. By the end of the season she was the main antagonist - cruel and manipulative. Actually, each different episode she felt different. Writers' fault much, probably.
Designated Hero: Quite frankly, all of the main characters from time to time, who continually behave in petty and selfish ways and never really learn from it or properly outgrow it. Some outstanding examples:
After Cleo gets fired from her job and Lewis takes the position, Rikki and Emma sabotage Lewis at his job in the hopes of getting him fired so Cleo can get her job back, which leads to Lewis being the prime suspect in a police investigation.
At the climax of the first season, when Lewis reveals he knew all along that the girls' loss of powers was temporary but Miss Chatham told him to keep quiet so their reactions would be real, Cleo responds by subjecting him to prolonged torture by trapping him on top of a water spout while the rest of the girls stand around laughing.
Despite knowing that Rikki is poor and lives in a trailer park, Emma and Cleo (who live comfy middle class lives) get angry with Rikki when they learn that she's trying to find something that has a reward attached to it.note In their defence of this one, they didn't know Rikki's father needed the money desperately and they assumed Zane was just being greedy.
Also Rikki, despite being poor, laughs at the simple idea of getting a job and barely even tries in Juicenet Cafe. She picks up something simple and illegal, instead.
Rikki, Emma, and Cleo sabotage a family dinner between Cleo's father and Charlotte's mother in an attempt to drive them, as well as Charlotte and Lewis, apart - never mind that at this point, Lewis was single because Cleo turned him down, and therefore fair game for Charlotte, who at this point has been nothing but a decent person.
After Charlotte's initial encounter with the moon pool, Lewis deliberately gets her wet to see if she'd gotten mermaid powers. Here's the kicker: they were in public at Juicenet. Not only would this have broken the Masquerade, but Lewis would have just exposed an innocent and confused teenage girl to the public if she had gotten mermaid powers. Neither he nor the girls seem to see any problem with this.
Designated Villain: Charlotte, who before going all-out evil doesn't really do anything wrong. Can you really blame her for getting a tad upset and suspicious when Lewis continually lies to her, or runs off or stands her up with little to no explanation to go and hang out with three other girls? To Charlotte's credit, in the beginning the show presents it more as Cleo being petty than anything else.
Fridge Horror: After Charlotte takes the locket and breaks Cleo's spirit - she swims out into a known shark breeding ground. Think about it: Cleo came close to committing suicide or at least some form of self-harm.
Now that Claire Holt and Phoebe Tonkin have become more well-known due to their roles in The Vampire Diaries and The Originals, Emma and Cleo's friendship is this.
Seeing Phoebe Tonkin as the meek one is very amusing when she would later get cast as bitches and Action Girls. And in Season 2 Cleo's Clingy Jealous Girl side does come out, which is almost Foreshadowing Phoebe's later casting types.
In the finale of Season 1 Cleo wonders if Dr Denman is gonna see if they can talk to fish. A few years later in H2O: Mermaid Adventures the girls can do just that.
Hollywood Pudgy: Some fans liked to mock Brittany Byrnes for her weight when she was on the show. Sure she was a little bigger than her three co-stars but was nowhere near fat.
Humour Dissonance: Emma invokes that's not funny at Rikki a couple of times in the pilot. In the instance where she says a joke Rikki made is actually funny - it's just a quip saying "this doesn't mean we're married, does it?"
Les Yay: It's a series about a group of teenage girls who often seem to like each other a lot more than their boyfriends. What do you think? (Polyamorous fics are...not unheard of.)
Moral Event Horizon: Charlotte crossed it when she in the second-to-last episode stole Cleo's locket and made her believe that Lewis no longer cared about her.
Stealth Pun: Since everything is water-themed, Rikki *might* be a pun on (show host) Rikki Lake.
The Scrappy: Good God, Kim. Many, many of the show's fans have expressed the deepest desire to punch her through a window for her constant attitude.
Some fans really like to hate Charlotte, espicially after her getting mermaid powers.
Suspiciously Similar Song: Score example; the theme that plays during emotional moments bears an uncanny resemblance, in both melody and instruments, to the main theme from Finding Nemo.
Take That, Scrappy!: Kim does get plenty of slapsticky comeuppance to make up for how annoying she is. She gets publicly embarrassed when she tries to out the girls' secret, catches the measles, gets sprayed with a garden sprinkler and is dumped by Elliot for being too bossy.
Testosterone Brigade: Mostly from season 2 onwards when all the leads got a Fanservice Pack. As the show is Australian and features stunningly beautiful lead actresses, there are frequent episodes that get them into bikinis, midriff tops, hot pants and short skirts. The show features a lot of episodes with parties, so there's plenty of reasons for the leads to get all dolled up.
They Wasted a Perfectly Good Plot: Some fans felt that there should've been a Season 3 episode in which all four mermaids appeared, which would've had both Emma and her replacement Bella interacting.
Toy Ship: One episode had Emma's younger brother Elliot trying to ask Cleo's younger sister Kim out. Kim just took advantage of him and kept bossing him around. He eventually got tired of her attitude and ditched her at the end of the episode.
Vanilla Protagonist: Emma is this, compared to the other two. Cleo has a Will They or Won't They? romantic teasing with Lewis, as well as having a fear of water. Rikki meanwhile has a mysterious backstory and it's a while before we even meet her family. Plus she too has Belligerent Sexual Tension and acts Tsundere towards Zane. Emma however is a well adjusted, straight-A student with a happy home life. Her romance plot gets solved rather quickly and the only real angst on her part is having to quit the swim team when she becomes a mermaid - and that's only in the second episode.