[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/makomermaidsah2oadventure.png]]
[[caption-width-right:350:Just add water. [[{{Spinoff}} Again!]]]]

->''In this world\\
We're all alone\\
You know I love my island home\\
We'll make this right\\
Find our way through this mystery!\\
I just wanna be\\
Swimming in the sea\\
Like it's just you and me\\
Forever, ever, ever\\
I just wanna be\\
With you, feeling free\\
It's my destiny\\
Forever, ever, ever\\
Together, forever, together\\
Lying in the sun\\
Together, forever, together\\
Just be you and me\\
I just wanna be...''
-->-- The ThemeTune

A {{Spinoff}} of the popular Australian fantasy series ''Series/H2OJustAddWater,'' ''Mako Mermaids'' follows the life of three mermaids and teenage boy turned merman. Sirena, Lyla, and Nixie were three young mermaids charged with protecting the small magical island of Mako during the full moon in order for the rest of their mermaid pod to perform their moon rituals. Unfortunately, young Zac falls into a mystical pool on Mako during a full moon and interrupts the sacred ritual, thus granting him merman powers, but causing the three young mermaids to be cast out of their pod. Equal parts comedy and drama, the series starts off with Sirena, Lyla, and Nixie attempting to remove Zac's powers so as they can rejoin their mermaid family while adjusting to life on land.

As of the second season, a few changes have been made to the cast line-up. Lyla and Nixie have left the show, and are replaced by two new mermaids named Mimmi and Ondina. A new merman, named Erik, is introduced as well. The second season follows the girls' continued efforts to remove Zac's powers, Evie's efforts to adjust to the changes in her life, and Zac and Erik's attempts to uncover the secret of the newfound Merman Cave on Mako Island.

The third season (fourth on {{Creator/Netflix}}, as the second season was split in two there), the mermaids have been reinstated into their pod, but continue activities on land with the pod's blessing. A new mermaid named Weilan arrives as a "foreign exchange student" from China, replacing Sirena in the main cast, but a dragon appears to have followed her, and it attacks merpeople every full moon. The mermaids and Zac take it upon themselves to investigate and stop the dragon before it can kill or depower the Mako pod mermaids, as it did to most of Weilan's.

The first through fourth seasons are available on {{Creator/Netflix}} and also premiered on Creator/DisneyChannel US on January 18, 2016.

----
!!''Mako Mermaids'' provides examples of:

* AbhorrentAdmirer: Chris' friend Karl has a massive crush on Weilan, who does not in any way return the feelings.
* ActOfTrueLove: Rita, the school principal, turns out to be a mermaid herself. She eventually reveals how, as a teen, she fell in love with a human boy, leaving her pod and living as a human herself to be with him but he died before they could be married. Despite that, Rita is clear she never regretted her choice.
* ActuallyPrettyFunny: When the other laugh at how Ondina fell on her ass after Sirena used lightning in their game, she reluctantly joins in.
* AdultsAreUseless:
** Viridia and the Mermaid Council, while well meaning, are all so locked in their prejudice against Mermen and Humans, that they're attempts to solve some of the situations often make the problems much worse.
** Averted with Rita however, whose advise and council to Zac, Evie and the Mermaids, often points them in the right direction when searching for a solution.
* AllLovingHeroine: Sirena is this in season 1 and 2. Mimmi becomes this in season 3.
* AllWomenLoveShoes: Nixie starts a fight with Evie over the "perfect shoes" in "Lyla Alone".
* AmbiguouslyEvil: Erik appears to be plotting something terrible, but he might just be interested in the Merman Cave because of its significance to merman history. [[spoiler:He sets forth a series of actions in the chamber after stealing Zac's powers that put all of the mermaids at risk. Granted [[AntiVillain he was trying to do it for a good reason]], to protect the mermaids with the power, but he completely ignored all evidence to the contrary and lied, schemed, and stole to get that far.]]
* AntiVillain: Erik, he does some pretty messed up shit to Zac, Evie, Cam and the Mermaids, [[spoiler: but he was doing what he believed to be for the greater good for his species, nor was he spurred by malice, and never realized just how much danger he was putting all of the Mako pod in.]]
* ArbitrarySkepticism: The pod doesn't believe Zac could have fallen from the ceiling as the main trio claim because there's no opening up there. Unless, of course, it was opened by magic. Which is a thing. That the mermaids know about. Because they're magic.
* ArchEnemies: By the end of season 2 Zac and Erik's hard friendship takes an immediate dive to nemesis. Can't really blame Zac after Erik [[spoiler:attacks his best friend, holds his sister hostage, steals his magic and takes possession and activates his cave on Mako.]]
* ArtifactOfDoom: It's claimed by the mermaids that the trident is a force of ultimate destruction and evil no matter who wields it. Naturally, it has to be destroyed.
* AscendedExtra: Evie becomes a mermaid in season 2 and becomes part of the main cast in season 2 and 3.
** She becomes human again in season 3, but she is still shown in the season 3 intro.
* [[AttentionDeficitOohShiny Attention Deficit....Ooh, Pretty!]]: Whenever Weilan goes shopping, she gets distracted by wanting to buy pretty clothes. Even when looking for artifacts that can be used to defeat an all-powerful sea monster.
* BathroomSearchExcuse: Evie wants to investigate the strange goings on by the residents of Rita's house, so she insists on tagging along with David's seafood delivery and then uses the bathroom excuse to wander the halls. She improves her odds by waiting for David and Sirena (who have a mutual crush) to be distracted by each other and asking Sirena, who is too lost in David's eyes to consider Evie's intents.
* BeautyBrainsAndBrawn: Sirena is beauty, very pretty and feminine; Lyla is brains, very intelligent and described as so by other characters; and Nixie is brawn, tough and impulsive. Later in the first season, Lyla and Nixie appear to switch roles, with Nixie being more reasonable and Lyla being more impulsive.
* BelligerentSexualTension: Most apparent in season 1:
** Zac and Lyla once their relationship devolved into a rivalry. During that time, they would constantly tease and taunt one another, while also complementing the other's intelligence in secret. Even after Nixie causes a LoveEpiphany by calling out Lyla's feelings for Zac, their relationship never evolves into anything more.
** Cam and Nixie also have an apparent rivalry with several moments of teasing, but they too never get together.
* BetaCouple: Cam and Carly, they receive a lot of attention after the two star dating.
* BigDamnHeroes: Zac gets one in in the season 1 finale [[spoiler:when he stops Cam from destroying the moon pool]].
* BlondeBrunetteRedhead: Sirena, Nixie and Lyla (subtle example as Lyla is strawberry blonde rather than having dark red hair)
* BookcasePassage: In the third episode the girls find one in Principal Rita's home that leads to a secret passage to the sea. The latch is, of course, a Relevant Book (it's about mermaids).
* CastingGag: The Spanish dub was directed by Elena Ruiz de Velasco, who played a couple secondary characters in the dub of ''Manga/MermaidMelodyPichiPichiPitch'', and it seems she couldn't resist the temptation to bring some of her former cast mates. Sirena is voiced by Carmen Podio, who voiced Mimi in ''Pichi Pichi Pitch'', while Carly is voiced by Sara Polo, who played Luchia. (Also, guest character Rikki is voiced by Belén Rodríguez, who voiced Karen, though Rodríguez already voiced Rikki back in ''Series/H2OJustAddWater'' a year before ''Pichi Pichi Pitch'' was distributed in Spain).
* CallBack: '''"Trust Issues"''' as the title suggests brings up Ondina's trust issues formed after Erik betrayed her, and projecting them on to Mimmi and Chris.
* CatsAreMean: Averted. Poseidon is generally well-behaved and approachable. When briefly turned into a human resembling Evie, he continues to act all pleasant and curious (if appearing exceedingly unusual to unaware humans). At times, the cat even appears quite confused over why mermaids keep freaking out in his presence.
* CharacterDevelopment: Cam's jealousy of the Mermaids and Zac, as well as some abuse he took for the latter turns him against everyone in the first season finale [[spoiler:where he nearly destroys the Moon Pool]]. By the second season, he eventually makes up with Zac, but gets tempted by Erik to again side against the protagonists. But this time, thanks to Zac and Carly, he keeps his moral center and remains an ally.
* ChildhoodFriendRomance: Zac and Evie were shown to have chemistry even as kids.
* CleaningUpRomanticLooseEnds: There seemed to be something largely hinted at between Zac and Lyla, and fans expected their relationship to develop more after the first season. However, with Zac and Evie as competition and Lyla's actress leaving the show, these loose ends were cleared up by writing out Lyla's character to have rejoined her pod.
* ContinuityCameo: [[Series/H2OJustAddWater Rikki Chadwick]] appears in the Season 3 finale.
* ContinuityDrift: It's clearly in the same universe as ''Series/H2OJustAddWater'', set just a few years later, and yet...
** In the first series there is a fairly ordinary, if surprising to the unwary, aboveground entrance to the Moon Pool chamber. It is open at all times. In the second series, the mermaids start out believing that there is no aboveground entrance. They learn better when the magic of the full Moon allows Zac (and, later, Cam) to fall through the roof of the cave and into the pool, but still without leaving any visible hole. For even more drift, in the last few episodes of the series, Rikki (from the first series) "visits" and says the cave hasn't changed from when she knew it, despite the absence of the old "sliding" entrance.
** Mako Island is the home of the "Mako pod" in ''Mermaids'', and it is established that the pod has been in the area for some time. But somehow the pod never encountered any of the mermaids from [[Series/H2OJustAddWater the first series]], despite both group's frequent visits to the island and to the Moon Pool. In contrast to Rikki's non-reaction to the former change, she is rightfully shocked to learn that real mermaids exist.
* ContinuityNod: Many situations and scenes are similar to the original series.
** Zac drinking floating bubbles of water from the air was originally done by Cleo.
** Like Emma, Zac had a promising watersports career which was brought to an abrupt end by becoming a merperson.
** When Zac tries to stop the surprise pool party, he starts to boil all the water in the pool away, which was done by Rikki to get revenge on Miriam for being, well, [[AlphaBitch Miriam]].
** Mimmi and [[spoiler:Zac's]] telepathic connection is identical to the one Neri, Mera and Charley shared in Ocean Girl, allowing them to see what the others were looking at. A double reference since in both cases, the connection is used by [[spoiler:siblings]].
** Like Rikki, Evie has only a father, their mother simply isn't around, though it is later explained that Evie's mom died sometime before the show.
** Evie using her moon ring to automate the domestic chores is similar to a scene from ''[[Series/AlienSurfGirls Lightning Point]]'' where Zoey uses her Luminan powers to do the same thing. In both cases, frustrated with how long it is taking, they decide to use an turboboost and naturally, it goes horribly wrong. (See also, of course, the Sorceror's Apprentice sequence in ''WesternAnimation/{{Fantasia}}''.)
** Wishful Thinking is an episode-long reference to ''[[Series/AlienSurfGirls Lightning Point]]''. They even reuse one of the stock photo props.
** Like Cleo, Mimmi gets a job at the local water park that involves using a cart to sell merchandise. And whenever they are rostered to feed animals near water pools, the level of waterproofing clothing they wear causes the other employees to wonder if they are mildly eccentric/crazy.
** Season 3 of both mermaid shows has the local hangout purchased with funds provided by the father of a male character (Zane and Cam) in order to save it from permanent closure with the additional motivation of intending this to give their sons business management experience. And the first decision of the new co-owner is to add a house band.
** Season 3 of both shows begins with the girls being attacked by magical water. In [[Series/H2OJustAddWater the old show]] it's a "water tentacle", in ''Mermaids'' it's a "water dragon". Both seasons end with their threats resolved in a highly positive way.
** Mimmi revealing her tail to Chris has a very similar feeling to when Emma revealed her secret to Ash.
* DangerousDeviceDisposalDebacle: Twice. The trident was supposed to "never be unlocked again", and later, [[spoiler:when Lyla hides it, it takes Zac all of an episode and a half to find it again]].
* DeadpanSnarker: Nixie is this for the season 1. Ondina for seasons 2 and 3.
* DeathGlare: Erik began delivering these towards the heroes by the end of Season 2, including a downright spine tingling one towards Carly after she splashed him from behind to rescue Cam from his telekinesis.
* DemotedToDragon: Cam becomes this to Erik in season 2. Though he is a mix of this and TheStarScream. He later betrays Erik because he wants to remain friends with Zack and his mermaid friends.
* DefrostingIceQueen: Lyla is definitely the harshest of the three leads at first.
** Ondina qualifies as well.
* DePower: The water dragon can do this to mermaids, as seen with [[spoiler:Evie]]. It has an opportunity to do this to [[spoiler:Mimmi]] and only ''doesn't'' because [[spoiler:the dragon is actually a cursed Nerissa, who won't attack her own daughter even in dragon form.]]
* DrillSergeantNasty: When Zac asks Weilan to teach him Turn the Tide, this is how his training session goes. She makes him practice the basic stance 180 times without pausing while she does nothing more then sits on a rock and counts how many times he does it correctly.
* ElementalPowers: Much like in the original series, Mermaids have a whole host of sea and storm related powers that allow them to control [[MakingASplash water]] and [[BlowYouAway wind.]]
* EquivalentExchange: Blown to pieces between the nineteenth episode and the twenty-third. [[spoiler:The trident charges up by partially draining one moonring, is used a few times, and yet it still has enough power to charge up three moonrings.]]
* {{Fanservice}}: Given that all the mermaids are all very, very pretty young women, and both of the mermen are handsome hunks, who all often showcase their very toned and well built bodies as merpeople this applies. Even their human friends, like Cam, Carly, David and Chris, are all very attractive as well.
* FriendlyRivalry: Nixie and Lyla in season 1, Ondina and Sirena in season 2 and Ondina and Weilan in season 3.
* TheFriendNoOneLikes: Cam in season 1 and Erik in season 2 are this. Besides being the BigBad of their respective seasons.
* FireForgedFriends: Cam with the mermaids, after Erik offers finally giving him a tail in return for his help, Cam outright states he wouldn't want one if it meant hurting the mermaids, [[spoiler:and returns the trident stone to their custody.]]
* FishOutOfWater: Mermaids Out of Water: The girls' first voyage on land is a literal interpretation of this trope.
* FiveStagesOfGrief: In "A New Man" Zac struggles to come to terms, [[spoiler:after learning he’s a real merman, he's adopted, and Mimmi is his sister,]] and goes through this process. [[spoiler:Denial, he acts like he's okay while avoiding his parents and Mimmi. Anger, he expresses to Evie his frustration about how he thinks everything in his life was a lie, refuses to accept Mimmi as his sister, and won’t let anyone help him. Bargaining, he decides to use his powers against a pair of obnoxious lifeguards to himself feel better, before Mimmi talks him out of reminding him, even though the Blakelys aren’t his real parents they still love and care about him. Depression, he becomes sad and finally decides to talk to his parents, who tell the story about how they adopted him. Acceptance, after talking to his parents, Zac reconciles with his friends, and accepts Mimmi as his sister, much to her happiness.]]
* ForcedTransformation: Ondina accidentally ends up turning Erik into a duplicate of Poseidon when practicing Mimmi's duplication spell.
* FromNobodyToNightmare: Cam in season 1 and Erik in season 2.
* FreudianTrio: in the first few episodes it seems that Nixie is the Id, Lyla is the Superego, and Sirena mediates between the two, but the remainder of the series seems to have Lyla and Nixie reverse roles.
* GreenEyedMonster:
** Cam towards Zac and the mermaids. He wants a tail so badly he was willing to betray them all, and steal the trident in his bid to gain one for himself.
** Erik has this reaction towards Zac in relation the Merman Cave. While Erik believes the Merman chamber belongs to all Merman, it becomes clearer and clearer to his growing resentment, that Zac is the only one who can activate it, as by right and bloodlines, it belongs to Zac and no one else, [[spoiler:causing Erik to finally snap, and steal Zac's magic, and activate it when Zac refuses to]].
* GreatOffscreenWar: Sometime before the start of the show, there was a great war between mermaids and mermen, which is why most of them today have considerable animosity for one another.
* HateSink: Joe, David's brother, never gets any positive character development, his presence tends to make things worse for the main characters, and none of the main characters like him--not even David, who speaks to him in an irritated tone most of the time and celebrates when Joe has his boat impounded.
* HoldingHands: A very consistent form of affection between Zac and Lyla.
* HumanityEnsues: Though completely voluntary, and still not ''quite'' human, when they first take human appearance, the girls have a hard time figuring out walking and spend their first episodes getting used to human traits from what to eat to going to the bathroom.
** One episode sees Poseidon (Rita's cat) accidentally transformed into a copy of Evie. Poseidon doesn't even seem to notice that a change happened, but his/her odd behavior, and the fact that many characters claim to have seen Evie in places Evie knows she wasn't, cause quite a bit of confusion for the rest of the cast.
** [[spoiler:It's later revealed that Zack was born as a merman; his mother transformed him into a human using a powerful spell that couldn't be broken by contact with water until he fell into the Moon Pool.]]
* HumansAreSmelly: One mermaid, after living on land for a while, comments that land people are actually quite bearable...once you get used to the strange smell.
* IAmWho: It turns out that the reason Zac is able to manipulate the Merman Cave is because [[spoiler: he was always a merman, and the trip to the moon pool broke the spell keeping him human.]]
* IdiotBall: Everyone gets a turn passing it to each other at times. Literally half the plot problems and conflicts in the first season are misunderstandings that could be solved by the characters stopping the "We can't explain it/It's too complicated" justification and actually explaining things to each other. It gets especially bad when characters refuse to explain the fantasy elements to those who are already aware of the in-series magic to begin with.
* ImHavingSoulPains: At the end of the third season [[spoiler: all the mermaids experience this when Erik activates the merman chamber. ]]
* InvoluntaryShapeshifting: Just like the original series, whenever the Mako Mermaids, or Zac, Evie, Erik or Rita get splashed with water, they only have 10-seconds before they sprout their tails.
* IslandBase: The mermaids use Mako Island as their go-to hideout.
* IslandOfMystery: Mako Island is home to a number of weird things, including the Moon Pool, the Merman Cave, and the cave that leads to the trident's storage area.
* ItsAllMyFault: Weilan blames herself for Evie [[spoiler: losing her tail to the dragon]] yet Evie assures her it isn't anybody's fault, and that she has every intention of remaining friends with the Mermaids, [[spoiler: and reminds them that she's an excellent free diver, meaning they can all still swim together whenever they want to.]]
* JerkWithAHeartOfGold: Nixie is this for the orignal mermaid trio. Ondina later takes on this role in seasons 2 and 3.
* {{Jerkass}}: David's brother, Joe. Just in his first appearance, he sees an unusual blip on sonar (a mermaid) and decides he just has to chase it down and find out what it is despite it obviously doing its level best to get away from him. He also treats David like shit at every opportunity, even callously taking his share of the cafe out, forcing David to close, because he thinks he can make more money buying new equipment for his trawler.
* JerkassHasAPoint: Cam can be a ManipulativeBastard, but when he says he feels thrown under the bus a lot for being a thankless SecretKeeper, his wishes to be [[IJustWantToBeSpecial let in on]] on the magic have merit.
* KeepingSecretsSucks: Pretty much every merperson in the series deals with this, but some instances in particular are
** Lyla wanting to tell Zac that she, Nixie, and Sirena are mermaids
** Zac wanting to reveal his merman secret to Evie
** Sirena wanting to reveal her secret to David
* LadyLand: Mermen exist, but are sent to live among humans, leaving only the females in the pod. [[spoiler:After helping save the island from Erik's power trip, Zac is admitted into the pod.]]
* LethalChef: In an attempt to calm Mimmi's hostile mood, Ondina makes crab pancakes for her as a peace offering. Not only are they charcoal burned, they're hard as a rock too. And apparently this is a common occurrence, whenever she prepares food, immediately a vote is cast unanimously to go and eat at the Ocean Cafe.
* LocalHangout: The Ocean café.
* LockedOutOfTheLoop: Evie spends much of Season 1 questioning what is going on with the main trio and what it has to do with her boyfriend.
* LongLostRelative: Late in Season 2, [[spoiler: Zac and Mimmi]] learn that they are siblings.
* LovableAlphaBitch: Nixie and Ondina.
* LoveInterest: Sirena and David. Zac and Evie. There is some ShipTease between both Nixie and Cam and Lyla and Zac that ultimately goes nowhere; once both girls leave the show, Cam winds up with Carly and Zac remains with Evie. Mimmi and Chris and Ondina and Erik for the season 2 cast. Weilan from season 3 never gets a love interest, despite Karl's attempts at winning her over.
* LoveTriangle:
** Sirena, David, and Carly: Carly likes David, but David and Sirena are clearly head over heels for each other.
** Zac, Evie, and Lyla: With Zac and Lyla spending so much time together after she "finds out" his secret, Evie [[MistakenForCheating believes, for a while, that Lyla and Zac are seeing one another behind her back]].
** Zac, Evie, and Weilan: Similar to the previous situation, however Zac and Weilan confirm they have no feelings for one another, whereas it is strongly suggested that Lyla had feelings for Zac.
* {{Lunacy}}: Genuine mermaids (Evie is not one) get the energy for their magic from the Moon Pool, and one can become a mermaid (or in Zac's case, regain his merman powers) by being in the Moon Pool on a full moon. Furthermore, inexperienced merfolk can be overwhelmed by the full moon's power, lapsing into a trance or drugged-like state.
* MagicalGirl: Seven of them, and two magical boys.
* MagicPants: During the shift from human to merfolk form not only do clothes disappear until they become human again but any hair decorations and hair spray also disappear, leaving the transformee's hair untied. Only moon rings are shown to carry over during the transformation, [[AWizardDidIt likely due to their magical nature]].
* MagneticPlotDevice: For some reason, the mermaids just can't seem to keep people off Mako Island.
* ManipulativeBastard: [[spoiler:Cam becomes this]] in the final three episodes of the first season.
* MeaningfulName: By the boatload. Nixie is a Germanic water creature much like a mermaid. Sirena is related to the Greek Sirens, which are sometimes mistaken for mermaids. One origin of the name Lyla is a term to refer to someone who is from an island. "Ondina" is a genus of sea snails; it is also a variant of "undine", a mythical water-related elemental being.
* MermanityEnsues: In contrast to its sister series, this time a merman is created when a human man named Zac falls into the pool on Mako Island during a full moon. Three mermaids are forced to watch over him as punishment.
* MisplacedRetribution: Zac falling into the Mako pool certainly isn't the girls' fault, but the other mermaids assume it is and banish them.
* MrFanservice: Zac and Erik, by virtue of being mermen.
* MuggleBestFriend: Cam, Carly and David to Zac, Evie and the Mermaids.
* MyGodWhatHaveIDone: One look at Ondina [[spoiler:dying]], and Erik immediately realizes how huge a mistake [[spoiler:activating the Merman Cave was.]]
* MyHovercraftIsFullOfEels: When Zac asks Mimmi to teach him a phrase in Humpback Whale, he repeats the sound and the mermaids laugh at him. Mimmi explains that he just told Ondina her feet are cute. Further attempts at getting the pronunciation right result in the mermaids starting a 3 way pillow fight just to get him to stop trying.
* NatureTinkling: What leads to Zac discovering the Trident Cave in the first episode. While camping with Cam on Mako Island, he goes deep into the jungle at night in order to relieve himself. He just so happens to pee near the cave as it opens up because of the full moon.
* NeverSayDie: Even when the crisis at hand is [[spoiler:all the mermaids dying]], the euphemism "destroyed" is used.
* NiceGuy: David.
* NiceMeanAndInBetween: The dynamic between the Mako Mermaids...
** Sirena as the Nice, Nixie as the Mean and Lyla as the In-Between.
** Sirena as the Nice, Ondina as the Mean and Mimmi as the In-Between.
** Mimmi as the Nice, Ondina as the Mean and Weilan as the In-Between.
* NotSoForgottenBirthday: Zac plans a secret surprise birthday for Evie, but by pretending he'd forgotten, he actually causes her to become depressed. It gets more complicated when Mimmi is recruited unexpectedly to keep Evie from going to where the party is being set up, given her almost complete ignorance of human customs.
* NotWhatISignedOnFor: After Zac witnesses the trident hurt Lyla, he backs out of his and Cam's plans to gain power through the trident.
* OfficialCouple: Zac and Evie are established as a couple and remain together for the entirety of the series.
* OneGenderRace: Averted in Season 2, when it's revealed that mermen are alive and well - they just live separately from mermaids. How either race reproduces, having lived many generations without contact with the other, goes unexplained.
* OnlyTheWorthyMayPass: Only a "true" merman can get into the merman cave.
* OOCIsSeriousBusiness: It is an indication of how bad your personal relationship with Mimmi is when she stops being nice, opting for direct animosity or confrontation.
* OrganicBra: In mermaid form, the girls have scales in exactly the same pattern as a bra, complete with straps. The mermen on the other hand only have scales on their tail.
* OurMermaidsAreDifferent: Like in the original series and films like ''Film/{{Splash}},'' a dry mermaid has human legs and a wet mermaid has fins. Mermaids also hold ElementalPowers and magic, and there are different varieties of regional mermaid. At their top speed, they look like torpedoes zipping through the water, and Nixie states that she can swim all day and night without stopping.
* PowerIncontinence: Happens when mermaids get colds, as it turns out.
* PutOnABus: Lyla and Nixie are mentioned to be out searching for a new home for the Mako Pod at the beginning of Season 2, and Sirena is stated to be on vacation with her sister in season 3.
* PuzzleBox: Weilan and Ondina try to enchant a Chinese puzzle box to trap the water dragon. Unfortunately, Poseidon, a teacher, and a cat all get sucked into it, forcing Weilan to open the box. They then decide that the box is too dangerous and destroy it to prevent another mishap.
* RequiredSpinoffCrossover: [[spoiler:Creator/CaribaHeine returns as Rikki]] in the fourth season.
* RevolvingDoorCasting: Despite the show ostensibly revolving around a trio of mermaids, that trio never stays consistent; Season 2 replaces Lyla and Nixie with Mimmi and Ondina, and Season 3 replaces Sirena with Weilan, resulting in a completely different main cast at the beginning and end of the series. The supporting cast remains far more consistent.
* RoyalBlood: Zac, [[spoiler:and to a lesser extent Mimmi]], learns that [[spoiler:through their mother, Nerissa]] are descended of the Mermaid and Mermen that ended the great merman-mermaid war and ruled over the sea in peace. Therefore, contrary to what Erik believes, the Merman chamber, that was built by the merman king, is his and his alone, and only responds to his magic.
* RunningGag:
** Carried over from the original series, a merperson falling to the ground if the transformation is unexpected.
** A mermaid seeing Poseidon (Rita's pet cat) for the first time, reacting with panic, and usually screaming. Subverted with Weilan, who loves cats and immediately starts cuddling him, but Weilan is already accustomed to life on land by that point anyway.
* SarcasticConfession: When Chris enquires about how Mimmi knew a recently rescued dolphin was about to give birth, Mimmi (who speaks dolphin fluently) replies with complete honesty "I asked her". Chris laughs and assumes she's making a joke.
* SceneryCensor: In Season 1 Episode 2 "Getting Legs", when Sirena, Nixie, and Lyla first get their legs, the camera pans away from them and a conveniently-placed tree branch hides the fact that the girls are naked.
** This trope is only used in this episode with all other natural-born mermaids getting their legs offscreen and their first scenes with legs having them already fully clothed.[[note]] For good reason in one case, as the mermaid in question was only about 10 years old. [[/note]]
* SecretChaser: "Evie Times Two" ends with Evie so perturbed by the actions of the main trio that she resolves to find out more about them.
* SecretKeeper: Cam is this for Zac. It's particularly hard for him to be so, because Zac initially wants to reveal his powers and be a superhero. [[spoiler:Lyla manipulates events so the mermaids also become this for Zac, but they already knew he was a merman]]. Later, Evie becomes one as well, before becoming a Mermaid herself, followed by Carly, David and Chris learning their friends secrets as well.
* ShipTease: Lyla and Zac were heavily teased with several moments of hand-holding and intense gazes. Cam and Nixie were also teased, given how Cam called her "cute" and "pretty."
* ShirtlessScene: Just scroll through a random episode and you're guaranteed to find at least one of these.
* ShoutOut: They really like their ''WesternAnimation/{{The Little Mermaid|1989}}'' references.
** Aquata is the name of another mermaid who was also a sister of a main character (Ariel) in the Little Mermaid.
** Erik also shares a name with a Little Mermaid character.
** In season 3, they keep using the phrase "little mermaids" when referring to Ondina's students (she was given the job of teaching junior mermaids).
* SmugSnake: Cam and Zac are this for quite a while.
* SpeaksFluentAnimal: Rita, Sirena, Nixie, and Mimmi (and ''not'' Lyla; Ondina and Weilan never have the opportunity) can all speak the language of dolphins. Mimmi is also fluent in the language of several types of whale and, apparently, some species of penguin.
* SpoilerOpening: The fact that Erik is a merman might have been a pretty major plot twist if they hadn't shown him with a tail in the opening credits.
* StumblingInTheNewForm: When most mermaids first walk on land they have trouble standing up for very long and their brand new leg muscles ache from the lack of use, the exception being Weilan who grew up spending plenty of time on land hiding from the Water Dragon.
* SuddenPrincipledStand: Zac's obsession with power suddenly halts the moment [[spoiler:he seriously injures Lyla with the trident.]]
* SurprisinglyRealisticOutcome: In "Lyla Alone", when Sirena and Nixie try to buy new clothes from Evie's shop with Rita's doubloons. When Evie discovers how they paid for the clothes, she not only refuses to accept the doubloons and returns them to the girls, she threatens to call the police if they do not pay her properly the next day.
** Erik gets fired by Carly after he skips work one too many times, her decision being backed up by David after he returns from his business seminar. Shirking your job despite putting in a good effort when you do show up for work will still get you fired.
* SuspiciouslySimilarSubstitute: Stubborn and cautious Lyla, for Emma; naive Sirena, for Cleo (with better non-magic singing skills, actually); and down-to-earth and impulsive Nixie, for Rikki.
* ThickerThanWater: [[spoiler:Mimmi's]] immediate reaction to finding out [[spoiler:Zac]] is her brother is to defend him from Veridia, knowing she'll be exiled for it.
* TookALevelInKindness: Zac, Cam, Evie, and Carly in season 2.
* TheChosenOne: Zac. He is openly called it towards the end of the second season and the last episode of season two is even called The Chosen One.
* ThisIsUnforgivable: Ondina justifiably has this reaction after Erik's actions, [[spoiler: endangered her pod and their friends, after he promised not to mess with the Merman cave.]]
-->'''Ondina''': ''(to Erik)'' You had a choice. Me or the chamber...you chose the chamber.
* TrueCompanions: While their relationships were initially rocky to begin with, by the end of season 2 with every one of them in on the Mermaids' secret, the core group (Zac, Evie, Cam, Carly, David, and the Mermaids) all have a good rapport with each other and consider the others to be good friends of theirs.
* {{Tsundere}}: Ondina is described as "prickly" and has poor people skills, but she's fiercely loyal to Mimmi [[spoiler:even over the pod's Council]] and eventually starts showing her softer side to Erik and (non-romantically) Weilan.
* WhamLine: "Do you realise what would happen if [[spoiler:the son of Nerissa]] controls the power of this place?" Followed by Mimmi asking "What does this have to do with my mom?"
* WhamShot: In the third episode, the girls are breaking into the house of Rita, the stern school principal, to get back a confiscated moon ring. They find a secret passage leading to an underwater cavern, wondering why a principal would have a cave linked to the ocean...and up swims Rita in mermaid form, who's dumbstruck to see the trio staring right back at her.
* WillTheyOrWontThey: Zac and Lyla went from loving gazes and hand-holding to constant bickering and teasing. Their up-and-down dynamic raised this question in the first season.