The two girls begin to explore their powers, but one day comes when Kelsey, an overachiever who excels at most subjects, comes to work on their science project and becomes jealous that Amy has been spending so much time with Brenna instead of her. When Amy goes running upstairs at her Christmas party, Kelsey follows her only to faint upon seeing Amy with mermaid tail. Plagued by nightmares, she confronts Amy, who reveals her secret, and suspecting Brenna is a mermaid, she pours water on the other girl, to find that she was right. Metaphorical cat out of the metaphorical bag, Brenna and Amy decide to show Kelsey their powers as well. Kelsey, intrigued, wishes to be a mermaid as well, but is disappointed to have Amy and Brenna say otherwise. She makes the two girls a scrapbook, which Amy evidently drops in the water at the pier. Kelsey sets of to find the scrapbook, only to be knocked unconscious and rescued by Amy and Brenna, who pull her up into the cave.
Amy wakes up to find it raining outside despite it never raining that time of the year, and her tail spontaneously appears without touching water. At Brenna's house, it's much too hot and her tail randomly appears as well, now yellow. Kelsey's room is freezing even though the thermostat reads 82 degrees, and she pops her tail for the first time. The three girls meet up at the park, telling each other that their powers aren't working, and later meet up at Brenna's house to discover that they each have a different power. Amy has water (manipulation of water), Brenna has heat (fire, boiling), Kelsey has ice/freezing. One day while swimming, they encounter a girl named Blaire (Tessa) whose mother was a mermaid (the genes skip a generation), and her mother abandoned her and her father to live in the ocean. The girls struggle with keeping the secret at Amy's birthday, discover their tails have disappeared for a day, Brenna has a few seeing Red moments, they find three crystal necklaces and Tess nearly learns the girls' secret.
Amy tells Tess about them being mermaids, thinking it will make Tess trust her after she, Brenna and Kelsey knock her unconscious under the spell of the eclipse. Tess, however, sends information to a marine lab revealing their secret. The girls try to follow her, but are unsuccessful. They later learn that Tess didn't go through with it and has been grounded. One day, stuck inside because of the rain, Kelsey and Brenna begin to turn on Amy. All is well until Blaire returns from Key Largo, not wanting to reveal anything, and Brenna and Kelsey bring to fight. Amy throws herself in between the two of them, and their concern for Amy counteracts their anger for each other and they make up. Amy's cousin Andy comes over, and the girls race to find her and find out what they did the previous day.
Has it's own Character and CMOF pages.
- Acting for Two: Christine plays the main character Amy as well as a newscaster. While the newscasts are usually separate from the main show (and may or may not be canon), the three girls watch a newscast about a fire that they think Brenna may have started in In the Wake.
- Adults Are Useless: Borders on There Are No Adults. The only adults to appear only appear for a scene or two. So far the only adults have been Amy and Tess' mother, Brenna's mom, Amy's aunt and Blaire's dad. Also, Bridget briefly plays Kelsey's mother in Power Hour, whose only purpose is to comfort Kelsey from a nightmare.
- An Ice Person: Amy at first, then later Kelsey.
- Attention Deficit... Ooh, Shiny!: Blaire on a regular basis, although the others have their moments of this as well.
- Beach Episode: The Lost Episode, The third and fourth Season Finales all feature beaches in them.
- Brought Down to Normal: In Scarce Scales the three girls lose their tails briefly.
- Break the Cutie: Poor Blaire. And Tess
- Break the Haughty: Tess after the third Season Finale.
- Broken Bird: Blaire, although it's more shown in Season 4. Tess after her Laser-Guided Amnesia.
- Cloud Cuckoo Lander: Blaire once again.
- Control Freak: Kelsey has shades of this at times.
- Cry Cute: All three girls do this in "Birthday Splash".
- Death Glare: Brenna has a very scary one. All three of them give a down-right creepy one to Tess in the Season 3 Finale.
- Dishing Out Dirt: Blaire's mom.
- "Do It Yourself" Theme Tune: Christine wrote and recorded one with her cousin, and sings a cover of Swimming by Florence + The Machine (in Season 5, Emma sings it with her.)
- Eerie Pale-Skinned Brunette: Amy and Kelsey have shades of this.
- Floating Water: Amy occasionally does this.
- Hollywood Nerd: Kelsey.
- Playing with Fire: Amy could boil water at first, but Brenna receives this power later on. Her power ranges from hot air to literal fire to boiling water.
- Parental Abandonment: Although she has an excuse, Terra left Blaire and her dad on her daugter's first birthday.
- Put on a Bus: Blaire in Season 5.
- Kick the Dog: Amy's treatment of Kelsey is very unnessisary in Season 2.
- Kick the Son of a Bitch: The girls teach Tess a real good lesson in the Season Finale.
- Nerds Are Sexy: Kelsey. Terra is also an example due to all the research on mer-genetics in Season 3.
- Nice Job Breaking It, Hero!: Amy is the main reason Brenna and Kelsey became mermaids. Plus there's the fact that Tess found the scrapbook that had pictures of her sister and her friend as mermaids which Amy knocked over and attacked her (although she did it unwillingly) and kept the fact that Blaire was developing powers in ALL OF THE FREAKING FINALES!
- Nice Job Fixing It,Villain: Tess' plan to expose her sister backfired in so many levels.
- NotSoHarmlessVillain: Tess in Season 5.
- Rapunzel Hair: Amy and Kelsey.
- The Stoic: Kelsey is the Only Sane Man of the group, minus her little freak outs and her Sanity Slippage in Cabin Fever. Blaire as well.
- Sanity Slippage: The main plot in Cabin Fever and Tess in Season 5.
- Who Wears Short Shorts??: Amy and Kelsey seem fond of these clothes.