This is an interesting concept to a story. It gives me some strange Harry Potter vibes for some reason (maybe because of the my thought-relation with this and the mermaids). This also taps into my fear of deep dark water so...yeah, spooky.

There were some parts to this story where the grammar got to me so I had to re-read a few parts (that may just be me though) and I need more info on these characters and the backstory on this.

Hope you write more for this story because if this is it, I may just cry because this is something vastly different not just the plot, but structure wise also with the intro and the sizes of paragraphs being consistent with phenomenal breaks.

Nice!