If your best friend were about to move to Australia, and you only had a few days left together, you would try to lend assistance to a mermaid, knowing that anyone who helps a mermaid is granted a wish, right? I thought so.

(That doesn’t always work, by the way. When my grandma was sick, I helped a mermaid study for her GED and my grandma still died. Stupid mermaid.)

“Aquamarine” is a cutesy little comedy aimed at tweener girls, people who have never seen “Splash,” and people who don’t remember “The Little Mermaid” very well. It’s set at a Florida beach club, where 13-year-old best friends Claire (Emma Roberts) and Hailey (Joanna “JoJo” Levesque) are about to be separated when Hailey’s mom moves them Down Under for a job. The girls are on the brink of adolescence and are mocked by the prettier, slightly older girls who populate the beach around them. Splitting them up will be tragic.

Well, then, wouldn’t you know it, a hurricane (the small, fun kind, not the deadly kind) tosses a mermaid into the beach club’s swimming pool, which to my mind means that swimming pool was waaaaay too close to the shore. Hailey and Claire find her and learn her name is Aquamarine (Sara Paxton), and I wonder if the merfolk aren’t severely limiting themselves if they’ll only use names with watery connotations. Aqua is a pretty ordinary teenage girl (except for being half-fish) and has swum away from home because her dad was going to make her marry some undersea doofus.

“What’s that?” you ask. “The past participle of ‘swim’ is ‘swum’?” Yes indeed. I swim, I swam, I have swum. Doesn’t sound right, does it? But it’s true.

Anyway, Aqua tells us the merfolk think the concept of “love” is just a myth, which is pretty ironic coming from merfolk. But her dad is a reasonable merman (Ethel Merman?), and he says if Aqua can show him proof of true love before the wedding, he’ll let her out of it. That gives Hailey and Claire three days to help Aqua get a guy to fall in love with her, and for their efforts they’ll be rewarded with whatever wish they choose (“as long as it doesn’t violate the laws of nature,” Aqua says cheerily, which immediately makes you start thinking of things you could wish for that DO violate the laws of nature).

“But wait!” you say. “How can Aqua meet a guy if she can’t leave the swimming pool? And how can she even live in a chlorinated freshwater environment after being raised in the sea?” And to that I respond: You are so stupid. I mean come on. OF COURSE Aqua can leave the pool. All she has to do is dry off her fin and it turns into legs! Don’t you know anything about mermaids?!

Aqua immediately spots as her potential love interest a hunky lifeguard named Raymond (Jake McDorman), whom Hailey and Claire have admired gigglingly for ages. At 18-ish, he’s a little too old for them, but for Aqua he’s just right. And so the girls, aided by all the latest magazines, teach their new fish friend the fine art of chasing boys and making them like you.

Based on Alice Hoffman’s young-adult novel, adapted by John Quaintance (TV’s “Good Morning, Miami”) and Jessica Bendinger (“Bring It on”), and directed by first-time Elizabeth Allen, the film makes no attempts to appeal to anyone other than its primary demographic. But Hailey and Claire are good role models for young female viewers — they’re modest, honest and loyal — and Aqua’s confidence, glamour and otherworldliness fills the need for a princess/fantasy figure. The movie does it what it does well enough, and without condescension or egregious illogic, to be simple, boy-crazy fun.

B- (1 hr., 43 min.; PG, a couple mild profanities, some mild innuendo.)