This is a crossover between My Little Pony: Friendship is Magic and H₂O: Just Add Water.

Twilight Sparkle, Fluttershy, and Rainbow Dash are swimming in the pool on Knacker Island under a full moon, and become mermares. They're not all necessarily very happy about it.

Also Flash Sentry is randomly a rich kid that nopony likes.

Warning: this story would be tagged [Random] [Comedy] if it had turned out to be funnier. It's kind of a silly parody crossover thing. If you want a sensible crossover between H₂O and My Little Pony, try H2O: Just Add Friendship by Jaded Naruko (or just stop wanting that).

Cover is based on art by tashiepie and toonham. Pre-read and made slightly less awful by Remedyfortheheart and Infinity Shade. ♥Thanks♥!