H20: Youngest Mermaid

Madeleine Hawkins is a sweet, young girl with an unfortunate disease known as Aquagenic Urticaria, or more commonly known as being allergic to water. All water, no matter the temperature or amount, has to do is touch her skin and she breaks out in hives, even her own sweat and tears cause a reaction.
One day, despite her condition, Madeleine sees two guys in the year above her trick a girl into getting into a broken boat before shoving it out to sea. Madeleine knows she has to do something and dives into the water and climbs into the boat. However she is unable to do much as she begins to break out in hives and pain erupts all over her body. She introduces herself to the girl, Cleo Satori.
One of her close acquaintances, Rikki Chadwick, manages to come in and save the day while also relieving some of Madeleine's pain. They pick up Emma Gilbert before deciding to take an amazing boat ride.
However they run out of fuel and get stranded on Mako Island, none of them realize that after that day their lives would be forever changed.