Ideas for mermaid series plot?

[MERMADES]

I need help thinking of a plot for a YouTube mermaid series I am planning. For example, in H2o: Just Add Water, the whole thing begins with Emma, Rikki, and Cleo getting stranded on Mako Island and discovering the Moon Pool that allows the whole series to keep going. I can't think of any unique way for my characters to become mermaids that isn't similar to any other show's idea, and I really don't want to feel like I'm copying it if I'm going to put in the effort to make this series happen. It's getting kind of frustrating XD So far all I could think of was they fell into some under water sand dune or something but I don't even think underwater dunes even exist, and if they do, I don't think you can fall in them.. Any suggestions?