This was from the Muggle Magic event that the Idaho Natural History Museum holds every year - I was friends with one of the coordinators on Twitter who asked if I could rustle up some people to be mermaids. (It was fantastic to get to meet someone I had previously only known in a digital space.) And of course I have friends who jumped at the chance! :) It was great fun, we spent the day playing music and singing (I actually played my ukulele! In front of people!) and making up mermaid songs. And decided that the proper collective noun for mermaids should be a "sparkle."
We borrowed the costumes from the Arts Quest program that runs fantastic theatre camps for kids every summer, you can find more information about the program here:
Arts Quest Theatre