Three teen girls are stranded on Mako Island, where a pool of water transforms them into mermaids in the series premiere of this animated version of "H2O: Just Add Water."

Emma enters a sand-castle competition. Meanwhile, Cleo looks after a challenging intern and rescues an injured sea turtle.

The girls find an old mermaid statue and intend to return it to an undersea wreck, but some treasure hunters may foil their plans.

A storm puts a birthday bash at a yacht basin in jeopardy, so the gals try to save the party and the birthday boy.

The girls try to halt the building of a luxury resort on Mako Island.

Emma is assaulted by some blue seaweed, which takes away her mermaid powers.

Lewis and the girls go to great lengths to stop the harm that discarded plastic bags are posing to the sea turtles.

An atmospheric disturbance leads to big trouble in Dolphin City and earns it the name "the new Bermuda Triangle."

Celebrities and a Hollywood production crew arrive in Dolphin City to shoot a movie, and trouble comes along as well.

Danny the octopus is snatched by an observation center, putting the upcoming volleyball tournament in jeopardy.

Lewis and the gals investigate some puzzling sound waves disturbing the whales, dolphins and mermaids.

A shark with a toothache seeks some relief onshore, but its presence could dampen Dolphin City's tourism season.

Rikki takes action after she spies on her dad and grows concerned about his relationship with his new girlfriend.