Rikki and Cleo face their final year of high school without Emma.
Bella tries to keep Will away from the Moon Pool; the Moon Pool has changed.
Cleo wants to be an assistant dolphin trainer; Rikki fires Nate's band.
Cleo puts Lewis' Valentine's plans on hold; Don dates a woman named Samantha.
Zane promotes the cafe with a dirt bike race.
Bella tries to start a relationship with Will, but sees that he's got another girl; Lewis tests the magic water at school and attracts the attention of the science teacher.
A picnic leads Don to end his relationship with Samantha until Cleo encourages him to pursue it; Sophie competes with Bella for a job and sets her sights on Zane.
Rikki and Bella hide out at Cleo's to protect themselves from a full moon water attack; Bella is kidnapped by a water tentacle; Lewis tries to keep Will away.
Will discovers that Bella is a mermaid.
Will is more interested in Bella as a mermaid than as a person.
Rikki receives counterfeit money at the cafe and is held captive by criminals on a boat; Bella and Cleo are forced to reveal the trio's secret to Will so they can rescue Rikki together.
Kim tries to derail Don and Samantha's wedding; Lewis receives an opportunity to study in America; Cleo realizes she's got to let Lewis live his own life and let him go overseas.
Zane challenges Will's free-diving skills; a unique crystal is found in the Moon Pool.
Sophie steals Bella's fundraiser idea; Samantha moves in.
Rikki is frustrated by the water attacks and goes to Mako Island on a full moon to confront the strange force in the Moon Pool; with Cleo and Bella delayed, Will pursues her and discovers she's been affected by the experience.
Cleo's introduced to Ryan, a young geophysicist who's working for Samantha; Rikki doesn't react well to Cleo consulting Ryan about the Mako rock and a fracture begins to appear in the trio.
Rikki fears Ryan will find out their secret when he begins spending more time on Mako Island.
Will gives up free-diving; Sophie kisses Zane.
Sophie becomes manager of the cafe; Bella can't stop sneezing.
Zane steals a Mako crystal to get Rikki's attention.
The girls take their final exams; the water force attacks early.
Bella wants to ask Will to the end of the year beach party, but thinks he has asked Rikki instead.
Cleo's dad gets a second job; Bella and Will try to find similar interests.
A comet is causing fish to flee from Mako Island.
The Moon Pool is damaged after the crystals have been harvested; a comet heads for Earth.
The girls' powers are enhanced during the full moon.
Emma uses her powers to help Elliott win at Soccer; Lewis decides to test the girls powers.
Zane is back and tries to win back Rikki; Cleo becomes suspicious of Lewis.
Rikki comes to stay at Emma's house and stirs things up.
Lewis tests a potion on the girls he found in an old book.
Don appears to have a girlfriend; Lewis becomes aware of Charlotte's feelings.
A dolphin goes missing at marine Park following a mermaid prank gone wrong.
Zane unknowingly has an argument with Rikki's father; Rikki must overcome her shame about her background.
Emma meets a handsome riding instructor; Emma must use her powers to heal an ill horse.
Charlotte is assigned as a tutor for Cleo; Cleo's attitude toward Charlotte drives Lewis away.
Zane enlists the girls' help to find a treasure under the ocean; Rikki is injured in the search.
Emma pricks her finger on coral and starts acting strangely.
Ash, returning as Juice Bar supervisor, fires Emma and then re-instates her; Ash asks Emma out.
Nate gets a potion irresistible to mermaids and all three girls go wild for him.
Elliot falls for Kim; Cleo and Lewis chaperone Elliot and Kim's date; Kim dumps Elliot.
Emma makes the girls promise to not tell Ash she's a mermaid; Ash and Emma kiss for real.
Zane and Ash fight while Rikki and Emma take sides; Cleo gets them back together.
Lewis' research leads him to Gracie's boyfriend from the 50s; Max tells Lewis to hold onto his love.
Charlotte discovers Gracie is her grandmother; Charlotte see film of Gracie as a mermaid.
Charlotte accuses Lewis of lying; Charlotte enters the moon pool and gets a tail.
The girls run into Charlotte as a mermaid; Lewis wants Charlotte accepted into the group.
Charlotte causes mischief; Charlotte picks on Cleo.
Rikki leaves the group; Zane tries to make Rikki normal.
Cleo runs away to the ocean; Lewis finds out what Charlotte has been up to.
The full moon rises, Lewis tries to lure Charlotte to the moon pool.
Three teenage girls discover a secret pool when they are stranded on Mako Island.
Cleo, Emma and Rikki fear that their secret will get out when they attend a pool party.
Cleo must overcome her fear of water in order to enjoy being a mermaid.
Lewis tests the girls' powers; Cleo's younger sister becomes suspicious when she reads Cleo's diary.
Cleo gets a job feeding the dolphins at a marine park; Emma has a sleepover party.
Elliot falls in love with Rikki after she saves him from drowning at the beach.
The girls ignore Miss Chatham's advice to beware of trouble when there is a full moon.
While trying to buy a fish for Cleo, Rikki finds herself involved in a fish-smuggling operation.
Zane and Emma each try to make their own short film to enter into a contest at the juice bar.
Byron persuades Emma to train him for a swimming competition; Rikki plays pranks on Lewis to try and unsettle him.
The full moon turns Cleo into a magical siren who attracts boys with her angelic voice.
Emma witnesses Miss Chatham arguing with Zane because she accidentally hit his jet-ski with her boat.
Zane believes that a mysterious creature is living under the sea and decides to mount an expedition to catch the monster.
Wilfred leaves Emma in charge of the juice bar for a weekend while he goes away to a conference.
A misunderstanding leads everyone to believe that Cleo and Zane are dating and planning on running away together.
When a rainy day traps the girls at Emma's house, they all pretend to be sick so that they do not have to go to school.
Rikki escapes to Mako Island after accidentally burning Emma during a full moon.
Cleo and Kim's relationship is strained when their manipulative cousin comes to visit.
Cleo tries to help Lewis win a fishing competition; Rikki and Zane are trapped together on the balcony of a fancy hotel.
Zane finds evidence linking Miss Chatham to a decades-old mermaid sea rescue; Zane pursues Rikki.
Emma and Cleo force Rikki to choose between her friends and Zane; Harrison plans to develop Mako Island into a tourist resort.
Rikki is furious when Miriam ruins her plan to buy an old locket from the local jewelry store.
Cleo and Emma hope that Lewis and Byron will ask them to the school dance.
Dr. Denman returns to do research on Mako Island; Emma tries to avoid going on a family beachside holiday.
The girls use the lunar eclipse to avoid being exposed by Dr. Denman.