Other Mermaids

Sirenele

The Romanian webseries Sirenele (The Mermaids) is a modern day fantasy show where a group of regular teenage girls gain the magical ability to turn into mermaids much like H2O: Just Add Water, which causes more problems than joy as they have to figure out how to live their lives while keeping it secret. The show is the creative vehicle of actress/singer/online personality Andra Gogan, who plays the main character, and her brother Răzvan Gogan. The show's ten bite-sized webisodes are all on youtube, though the series ends on a cliffhanger.

The show's lore is that the Mermaid Queen sent five magical medallions into the world that are destined to be found by those worthy of them. Three of them are found by Selena (Andra Gogan), Milen (Maria Dinu) and Lena (Daria Meluta), who become friends as they investigate what's happened to them and how their mothers are connected, while their enemies the Order of the Mermaid Hunters close in.

Sirenele: Secretul Medalionului

My impression from what I've seen online is that Andra and Răzvan Gogan intended to make a second season of Sirenele, but along the way this evolved into making a trilogy of movies instead, using some of the same characters and keeping the concept of teenage girls who become mermaids. It's possible that, when they obtained a bigger budget, they decided to make a soft reboot with better production values. And actual underwater scenes, too.

The first of the trilogy is Sirenele: Secretul Medalionului (The Mermaids: The Secret of the Medallion), which opens with the trio of Selena (Andra Gogan), Milen (Maria Dinu) and Lena (Daria Meluta) already friends and collectively hiding their mermaid transformation abilities, so it's sort of a follow-up to Sirenele, except it's only in this movie that the Order of the Mermaid Hunters get on the girls' trail when Selena is caught on camera in her mermaid form.

Being a mermaid is such a burden at this point that Selena is determined to get rid of her tail. She hears a voice in her head instructing her to go to the island of Elysia in Spain, and she makes the journey, with her mermaid best friends and Ricki (her crush in the webseries, but here seems to be more just a friend) following after a close call with the Order.

Many thanks to Jay, who let me know about this movie.