Based on the novel by Alice Hoffman, Aquamarine is a charming coming of age tale about the enduring power of friendship, which melds the fish-out-of-water comedy of Splash! with the sassy sensibilities of Mean Girls.

Screenwriters John Quaintance and Jessica Bendinger never talk down to their target audience teenage girls and they develop two strong, believable lead characters, whose journey of self-discovery is tinged with disappointment and tragedy.

The film has winning performances from Joanna JoJo' Levesque and Emma Roberts as the 13-year-old best friends, struggling with impending separation. The young actresses are perfectly matched, sparking off one another beautifully so the dialogue feels natural. They carry the big emotional scenes with aplomb. Sara Paxton invests a zany, offbeat quality to her perennially cheery mermaid and Jake McDorman gamely pokes fun at himself as the beefcake love interest, who isn't adverse to gratuitously flexing his muscles for a dreamy slow motion close-up.

The heroines of the film are Claire (Roberts) and Hailey (Levesque), who have been best pals for what seems like forever. At the end of summer, Hailey's marine biologist mother, Ginny (Cladia Karvan), is moving to Australia for her work and the youngster must reluctantly leave too. So the girls make the most of their final days in the sun, spying adoringly on hunky lifeguard Raymond Caldi (McDorman), who works at the beach club run by Claire's grandparents.

In the aftermath of a violent storm, Claire and Hailey discover an 18-year-old mermaid called Aquamarine (Sara Paxton) washed up in the club's swimming pool. Aqua, as she becomes known, desperately needs the help of the two girls. Under the sea, the beautiful mermaid is denied the prospect of true love. Her father has arranged a marriage "to a merman who's about as deep as a tidal pool", which must go ahead as decreed unless Aqua can show in just three days that such a thing as true love exists. Aqua sets her sights on Raymond and Claire and Hailey agree to help their new friend.

It won't be easy though. "All the girls are after him," sighs Claire, ". . . even a few boys". The competition includes bitchy rich girl Cecilia (Arielle Kebbel), who will stop at nothing to get Raymond to take her to the Last Splash end of summer party.

Plying a nice line in female empowerment, Aquamarine mines a rich vein in broad humour as Claire and Hailey tutor Aqua in the rules of teen dating, pooling knowledge from glossy magazines.