"H20: Just Add Water". The series that gave Claire Holt and Phoebe Tonkin their start. Sadly, for a TV series about mermaids and that features teenage girls living by the coast of Australia during the summertime, there's only a handful of episodes in which they wear cropped tops or bikinis like this. Talk about wasted opportunities!
https://www.youtube.com/watch?v=5JZ7WrwJpes