H2O: Just Add Water

Emma, Cleo, and Rikki are three teenage girls who discover they are mermaids and gain powerful abilities over water after finding a magical place, which dramatically changes their lives.

Miriam hosts a pool party, prompting Cleo to consider attending despite her fear of water. Emma reflects on her future in swimming, while Rikki uncovers something new.

Rikki, Emma, and Cleo learn that sea turtles are being trapped in fishing nets and try to free them. Their efforts to cut the nets lead a fisherman to believe a shark is loose in the ocean.

Emma decides against hosting her annual sleepover party after recent events, but Rikki and Cleo attempt to persuade her otherwise. At the same time, Lewis carries out experiments involving the girls.

Cleo's sister Kim discovers her diary and misinterprets its contents, believing Cleo and her friends to be "evil mermaids," and considers exposing them. At the same time, Lewis travels to Mako Island to investigate the events surrounding the girls.

Emma faces a babysitting challenge when her younger brother Elliot develops a crush on Rikki, and she turns to Lewis for assistance.

Miss Chatham warns Cleo of an impending danger she fails to fully comprehend, while Emma becomes trapped in a trance, unable to revert from her mermaid form during the full moon.

Lewis is presented with an exciting opportunity to work with a marine biologist, but the girls worry that his growing curiosity might lead him to disclose sensitive information.

Rikki is hired to gather rare fish, but her task becomes complicated when she discovers the employer is profiting from their illegal trade.

Rikki participates in a short film contest with the theme "Heroes" by using her powers to capture unique underwater footage. Meanwhile, Emma interviews her mother, and Zane and Lewis attempt to break Dr. Bennet's windsurfing record.

Byron enlists Emma to help coach the school's swimming team, leaving her conflicted about getting involved given her current circumstances. At the same time, Lewis continues his experiments on the girls, drawing Rikki's frustration.

Cleo gains the ability to hypnotize boys under the full moon, attracting an unexpected wave of admirers.

Emma invites Miss Chatham to stay at her home, and Zane accidentally overhears Miss Chatham expressing worries about "her treasure.

As Cleo's 16th birthday approaches, she worries her father will throw another embarrassing celebration. At the same time, Zane becomes determined to find the mysterious "sea monster" he encountered during a near-drowning incident.

Emma adjusts to her role at the JuiceNet cafe, but faces challenges when she is put in charge of her new and difficult employee, Rikki.

Cleo's friends and family speculate about the identity of her rumored boyfriend while she remains secretive. At the same time, Zane persists in investigating a mysterious sea monster he claims to have seen.

To avoid revealing their secret during a thunderstorm, the girls pretend to be ill, but their convincing act draws the concern of medical professionals.

Zane travels to Mako Island in search of a legendary sea monster. Meanwhile, Rikki struggles with losing control of her abilities during the full moon, and Zane discovers her in this condition.

Cleo and Kim find themselves in a difficult situation when they are left in charge of their cousin Angela, who insists on going body boarding despite Cleo's objections. Angela's persistence leads to a chaotic distraction involving local wildlife.

Lewis competes in a local fishing derby, but his lack of skill leads to trouble. Cleo tries to assist him, but her intervention backfires. At the same time, Rikki and Zane find themselves stuck on a hotel balcony.

Emma attempts to dye her hair red as part of a new look, but her half-mermaid heritage complicates the process. Meanwhile, Zane invites Rikki on a date, marking a new development in their relationship.

Emma and Cleo grow worried about Rikki's relationship with Zane and pressure her to choose between him and their friendship.

Rikki discovers a locket resembling Miss Chatham's in a jewelry shop and becomes determined to obtain it.

As the school dance approaches, Emma and Cleo anticipate romantic invitations from Byron and Lewis, while Miss Chatham and Lewis engage in a debate over the value of magic versus science.

Emma tries to avoid joining her family's annual vacation by making excuses, but they fall flat. At the same time, Zane gets closer to uncovering a girl's secret with the return of Dr. Denman.

Dr. Denman devises a plan to capture the girls on Mako Island, forcing Zane to confront a difficult choice about where his loyalties lie.

While a rare planetary alignment draws them back to Mako Island and causes unexpected changes in their powers, Cleo deals with challenging family situations at home as Lewis attempts to maintain stability.

The girls struggle to control their emerging powers, and Cleo becomes frustrated when Lewis fails to support her. A new student, Charlotte, arrives and quickly forms a bond with one of the group.

Rikki avoids Zane after his return but is forced to seek his assistance following a speedboat incident. Meanwhile, Charlotte's continued flirtation with Lewis causes Cleo concern over their secret.

Emma hosts a party to show she can be as fun as Rikki, causing unexpected issues. At the same time, Lewis attempts to assert his masculinity, and Cleo becomes intrigued by mysterious cards from an unknown admirer.

The Setori begin to experience troubles, and the JuiceNet is threatened by the opening of a new bar. Lewis discovers a book of mermaid spells, and the girls try using a potion to resolve the issues, but they find that handling special powers is more complicated than they expected.

Cleo becomes concerned upon seeing her father with another woman, only to discover it is Charlotte's mother. At the same time, Rikki and Emma try to use their powers to help the Sertori family's dinner go smoothly.

Cleo is unexpectedly fired from her job at the Ice Cream Stand, and her friend Lewis is hired as her replacement, surprising everyone. Rikki and Emma attempt to retaliate against Lewis but end up overstepping their bounds.

Zane becomes intrigued by Rikki's hesitation to share where she lives and eventually persuades her to show him her home, which is a trailer park where she lives with her gruff father.

Emma accompanies Eliot to horseback riding lessons, where his competitive nature leads him to try and outperform the instructor. At the same time, Lewis goes on a double date with Charlotte and Cleo.

Cleo begins to face difficulties at school and receives assistance from a new tutor. Meanwhile, Charlotte grows closer to Mako Island with Lewis's support, creating new complications.

Rikki, needing money, joins a search for a valuable lost statue but lies to Emma and Cleo about her plans. Her deception leads to trouble when she is knocked out during the mission.

Emma is poisoned after cutting her finger on coral and begins transforming into a white-scaled creature. At the same time, Charlotte grows suspicious that Cleo is trying to sabotage her relationship with Lewis.

Lewis, Emma, Rikki, and Charlotte join Cleo's family on a camping trip to Mako on the night of a full moon. As the lunar event affects the three girls, Charlotte's curiosity leads to complications they struggle to contain.

Cleo attempts to reconnect with Lewis and come to terms with her powers, while Emma is taken aback by the arrival of a new supervisor with ambitious plans for change.

Zane discovers a legend about Ambergris, a mythical perfume said to make mermaids fall in love with whoever wears it. After he purchases it, Nate ends up using it, causing Emma, Cleo, and Rikki to become infatuated with him.

Lewis becomes concerned after having a recurring dream about Cleo being photographed by strangers. He and Cleo later take Eliot and Kim to a marine park, while Emma begins to suspect that something is developing between Ash and Rikki.

With a full moon approaching, Cleo and Rikki fall under its dangerous spell, putting their secrets at risk when Ash unexpectedly visits Emma's house. Lewis must act quickly to prevent them from revealing their powers before it's too late.

To celebrate the first anniversary of becoming mermaids, Cleo organizes a party, but tensions arise when a conflict between Ash and Zane causes a rift between Emma and Rikki, threatening to leave Cleo without her friends.

Lewis investigates the moon pool and discovers that Max Hamilton conducted research on it decades earlier. He considers revealing the girls' secret to Hamilton in hopes of solving the mystery.

Charlotte questions Lewis about his time with the girls and initially accepts Cleo's explanation, but a clue from Max's research leads her to uncover a hidden truth. At the same time, Ash offers to help Emma overcome her fear of water.

Charlotte's determination and curiosity drive her to seek out Max, who validates her theories and guides her to the Moon Pool, while Lewis struggles to maintain stability in his personal life.

The girls agree to accept Charlotte into their group, and the four of them work together to join the volleyball team in order to pass their Physical Education class.

Charlotte is determined to demonstrate her love for Lewis and prove herself superior to the other contestants. When Nate creates problems for Lewis, she ignores their advice and takes direct action to resolve the situation.

Tensions rise during Lewis' birthday celebration, leading Charlotte to take charge and remove Rikki from the event. As the situation escalates, Charlotte must find a way to resolve the conflict and salvage the party.

Charlotte, upset about being excluded from the girls' circle, pressures Lewis to choose between her and his friends, leading Cleo to feel abandoned and run away. Lewis must ultimately decide where his loyalties lie—between Cleo and his friendship with her or his relationship with Charlotte.

A rare planetary alignment causes the full moon to drain mermaids of their powers if they enter the moon pool, but Charlotte remains unaffected. She attempts to expose the girls' secret before being taken to Mako Island by Lewis, prompting the mermaids to pursue them, leading to a confrontation.

Cleo and Rikki begin their final year of high school and form friendships with new students Bella and Will. Meanwhile, a mysterious new force emerges on Mako Island, capable of manipulating water to oppose the girls.

Bella attempts to steer Will away from discovering the Moon Pool by revealing information about Mako Island. Meanwhile, Lewis and the others learn that the Moon Pool has unexpected differences from what was previously known.

Cleo applies for a position as a dolphin trainer at the marine park, while Rikki takes action to stop Nate's band from performing at the cafe until Cleo and Bella resolve their conflict.

Cleo delays Lewis's romantic plans to assist Kim with her chaotic love life, while Don begins a relationship with Samantha, a National Parks Manager.

Zane organizes a dirt bike race to attract more customers to the cafe, but Rikki discovers it's a fraudulent scheme and teams up with Bella to expose him. At the same time, Lewis and Cleo uncover a fascinating discovery while experimenting with the waters of the Moon Pool.

Bella attempts to connect with Will, but her efforts are complicated when she unexpectedly encounters him with another girl at his home. At the same time, Lewis tries to secretly test the water from the moon pool, only to be discovered by his teacher.

Cleo's family and Sam enjoy a beach picnic, but Cleo's reluctance to approach the water causes tension. Meanwhile, Kim takes advantage of her father's good mood to receive numerous gifts. At Rikki's Cafe, Will's sister Sophie competes with Bella for a position Bella had hoped to secure.

While staying at Cleo's house during a full moon, Bella is attacked by a water creature, prompting the others to investigate. Meanwhile, Will returns to the moon pool, having realized a link between his earlier experience there and the full moon's cycle.

Cleo secretly experiments with moon pool water, leading to unexpected complications when her fish, Hector, becomes trapped in a floating water bubble. At the same time, Lewis finds himself in an awkward social situation, playing golf with Cleo's father.

Bella gives Will a fossil she found while swimming, which leads him to suspect it may be rare, prompting him to investigate further. Rikki becomes concerned that Will is getting too close to discovering the truth about their mermaid identities and urges Bella to avoid him.

Bella assists Will with his free-diving training, but becomes upset when she feels he is more attracted to her mermaid side than to her as a person. Meanwhile, Rikki and Cleo struggle to adapt when the cafe's first corporate event turns out to be a children's party.

Rikki is taken hostage by criminals on a boat after receiving fake money at the cafe. To save her, Bella and Cleo must convince Will to help by revealing the group's secret.

Kim tries to disrupt Don and Samantha's wedding plans, while Lewis is offered a chance to study in the United States, prompting Cleo to come to terms with letting him pursue his future abroad.

Will tests his limits during a free-diving challenge with Zane, while the girls find an unusual crystal in a rock from the Moon Pool.

Sophie takes credit for Bella's idea for a fundraising concert to boost the cafe's publicity, causing tension. Meanwhile, Cleo becomes caught between Kim and the new influence of Samantha in the Sertori household.

Rikki, frustrated by ongoing water-related attacks, travels to Mako Island under a full moon to investigate the mysterious force in the Moon Pool. When Cleo and Bella are delayed, Will follows her and realizes she has been affected by whatever she encountered.

Cleo meets Ryan, a young geophysicist working with Samantha, and begins consulting him about the Mako rock, causing tension with Rikki and straining their friendship.

Rikki is worried that Ryan's investigations on Mako Island might reveal their hidden secrets, but Cleo and Bella dismiss her concerns. Her attempts to prevent Ryan from discovering the crystals in the Moon Pool become increasingly desperate.

Will competes in the Free-Diving Championships but decides afterward to step away from the sport and distance himself from Sophie. Meanwhile, Rikki witnesses Sophie kissing Zane at the event and ends their relationship.

Zane appoints Sophie as head of staff at the cafe, giving her more authority. Bella experiences a sneezing allergy that unexpectedly activates her powers, and Sophie uses the situation as a reason to consider firing Bella and the band.

The Mako crystals are revealed to hold powerful energy, prompting the team to launch a rescue mission after Zane steals one in a misguided attempt to impress Rikki.

The girls take their final exams while dealing with an unexpected water-based attack triggered by an early rising full moon. They face the threat at the Moon Pool, where they receive a cryptic message related to Mako Island.

Bella plans to ask Will to the end-of-year party but becomes upset when she sees him talking to Rikki, leading to a misunderstanding that results in Will confessing his feelings for her. Meanwhile, Sophie attempts to convince Zane to rename their café.

Don takes a second job at the Marine Park's Pirate Ship attraction, where his performance draws attention and begins to overshadow Cleo's Dolphin Show, raising concerns about its future. Meanwhile, Bella and Will struggle to find common ground as they navigate differences in their personal interests.

Cleo discovers that a comet is driving fish away from Mako Island's waters, prompting the group to reactivate the message in the Moon Pool, which reveals the comet's impending collision with Earth. Meanwhile, Sophie teams up with Ryan and, with Zane's assistance, works to remove the crystals from the Moon Pool.

Sophie and Ryan's attempt to retrieve rare crystals causes damage to the Moon Pool. To avert a comet-related disaster, Cleo, Rikki, and Bella use their combined magic to protect the planet. The episode concludes with the girls unexpectedly graduating.