When Cleo, Emma and Rikki get stranded overnight on Mako Island, a magic pool changes the girls' lives forever.
While Emma competes in a sand castle contest, Cleo must babysit a high-maintenance intern and save an injured sea turtle.
The girls discover a mysterious and ancient mermaid statue and want to return it to an underwater wreck, but treasure hunters have other ideas.
When a storm threatens to wash out a yacht-based birthday party, Emma and the girls must save the day -- and the birthday boy.
Zane's father plans a luxury resort on Mako Island -- so the girls swim into action to save their beloved retreat from ruin.
An aggressive blue seaweed attacks Emma, reversing her mermaid powers and forcing her friends to come to the rescue.
When discarded plastic bags pose a threat to Teddy and his sea turtle friends, Lewis and the girls must take extreme measures to stop the menace.
An atmospheric disturbance results in some disastrous consequences in Dolphin City, which is now labeled as the new Bermuda Triangle.
Dolphin City is the location for a Hollywood movie, bringing big stars to town and causing star-crossed trouble under the sea.
When Danny the octopus gets captured by the Oceanic Center for observation, it causes problems with his friends and the volleyball tournament.
Lewis and the girls must find what's behind mysterious sound waves that create havoc with the whales, dolphins -- and mermaids -- of Dolphin Bay.
When Burke the shark breaks a tooth and wanders near the beach in pain, he causes a panic in Dolphin City that threatens tourist season.
After spying on her father and worrying that he might be making a big mistake with his new girlfriend, Rikki takes matters into her own hands.
Clownfish are disappearing from the bay, so the girls spring into action to find out why. Could a mysterious diver be the culprit?
When the stone circle causes Cleo to forget that she can turn into a mermaid, Emma and Rikki scramble to keep her from transforming in public.
When Lewis promises to tell his Valentine's Day sweetheart, Abby, a big secret, jealous Cleo fears he will give away the girls' mermaid identities.
The girls and Bobby the dolphin untangle a mystery when Bobby's twin, Robby, is captured by someone in a mysterious speedboat.
When her father goes to sea on a mission, Cleo's worries begin to affect her dreams. But could her nightmares be trying to tell her something?
Tired of the racket Miriam and Zane are making at their beach party, Bernie leaves his cave -- giving the Vandals a chance to move right in.
To protect the White Mermaid, the girls guide explorer Stanley Finch to the underwater stone circle, whose magic makes Stanley think he's a pirate.
When a spell forces Rikki to remain a mermaid until the next full moon, she has to find a way to lay low -- and underwater -- for three full days.
Lewis is thrilled when the university hosts an underwater robot competition, but the girls fret over the safety of their marine friends.
Emma's younger brother catches a glimpse of her mermaid tail and thinks he's seen a sea monster -- soon the whole town is in an uproar.
The mermaids turn to a cranky giant octopus for help when the Vandals invade the bay with a horde of stinging jellyfish.
Having played one too many practical jokes, Teddy can't get anyone to believe his warning that an underwater volcano is about to erupt.
Lewis joins a famous explorer in a high-tech submarine to hunt for a sunken treasure ship, but a mishap strands them at the bottom of the sea.