- Previous season: Season 2
When a Chinese mermaid named Weilan runs into the Water Dragon that destroyed her pod, she flees to Mako Island with the creature in pursuit. Mermaids Ondina, Mimmi and Weilan must defend Mako Island and the Gold Coast from destruction.
- Chai Romruen as Zac Blakely
- Isabel Durant as Ondina
- Allie Bertram as Mimmi
- Gemma Forsyth as Evie McLaren
- Linda Ngo as Weilan
- Dominic Deutscher as Cam Mitchell
- Taylor Glockner as Chris
- Kerith Atkinson as Rita Santos
- Rowan Hills as David
- Brooke Nichole Lee as Carly Morgan
- Mikey Wulff as Karl
- Summer Robertson as Ava
- Milly Walton as Jewel
- Emily Robinson as Amaris
- Savannah Foran-McDaniel as Naia
- Tasneem Roc as Nerissa
|A Visit From The East||May 27, 2016||01||3.01|
|Ondina is tasked with teaching the younger mermaids. A mermaid from China joins the pod. During a full moon ceremony, a terrifying beast emerges.|
|Seeing Is Believing||May 27, 2016||02||3.02|
|When marine park workers are sent to investigate the reported sea monster, the mermaids must create a credible explanation to stop further inquiries.|
|Recipe For Success||May 27, 2016||03||3.03|
|Weilan casts a knowledge transference spell on Zac Blakely to help him pass a biology test. But more than just science facts transfer from her body to his!|
|Mopping Up||May 27, 2016||04||3.04|
|When Evie tries to using her new moon ring to magically finish her chores, things quickly get out of control. Joe makes an upsetting announcement.|
|The Puzzle Box||May 27, 2016||05||3.05|
|Weilan comes up with the idea of using a Chinese puzzle box to trap the sea dragon. Cam panics when Carly suggests they take dance lessons.|
|New Beginnings||May 27, 2016||06||3.06|
|Evie's moon ring lesson with Ondina takes an unexpected turn. At the Marine Park, Mimmi discovers the reason for a rescued dolphin's distress.|
|Turning The Tide||May 27, 2016||07||3.07|
|Zac begs Weilan to teach him an eastern spell few have mastered, which he hopes to use against the dragon. Joe encounters a water ball.|
|The Way of the Dragon||May 27, 2016||08||3.08|
|On the eve of the full moon, Ondina and Mimmi defy Veridia's orders. Evie becomes suspicious when she spots Zac and Weilan meeting in secret again.|
|Reversal of Fortune||May 27, 2016||09||3.09|
|After overhearing Ondina blaming her for Evie's loss, Weilan runs off. Meanwhile, Mimmi and Ondina combine their powers to try to restore Evie.|
|Wishful Thinking||May 27, 2016||10||3.10|
|Zac realizes a shell he found has magical powers, and he accidentally sends the mermaids back in time five years, where they meet his younger self.|
|Lost And Found||May 27, 2016||11||3.11|
|While Ondina teaches the little mermaids to walk on land, her fastest-learning student wanders off and soon runs into Chris and Karl on the beach.|
|Trust Issues||May 27, 2016||12||3.12|
|When Mimmi and Chris go on a date at the beach, Ondina goes to great lengths to protect her. Cam tries to lure more upscale customers to the cafe.|
|Letting Go||May 27, 2016||13||3.13|
|Mimmi and Zac are startled by a mysterious yet strangely familiar vision. Cam's dual role as Carly's boss and boyfriend becomes difficult to manage.|
|Age Before Beauty||May 27, 2016||14||3.14|
|Weilan mistakenly makes tea for Rita using a magic growth accelerator. Can the mermaids cure Rita before Mrs. Trumble takes over principal job?|
|The Legend of Jiao Long||May 27, 2016||15||3.15|
|A priceless artifact discovered by a deep-sea treasure hunter provides a clue as to how the mermaids can defeat the water dragon.|
|Homecoming||May 27, 2016||16||3.16|
|The vision reappears to Mimmi and Zac, this time speaking to them. Weilan learns a new detail about the dragon legend that suggest Nerissa is still alive.|
- Linda Ngo became main cast.
- Cariba Heine appears in the season finale as Rikki Chadwick from H2O: Just Add Water.
- Production finished in July 2015.
- This season has the least amount of episodes.
- Evie loses her tail and powers in The Way of the Dragon.
- All three mermaids in this season are from separate origins: Ondina is a mermaid from the South; Mimmi from the North; and Weilan from the East.