This has definitely gotta be one my most favourite nail art I've ever done!!
I made it based on a painting we have up on our wall , I'll post the pic below:
I started off with a light blue base, then using a fan brush, i went across each nail a couple of times with white and a darker blue to get the water effect.
I then painted on the small fishes in yellow, and then went over it with red. I used a dotting tool to make the eyes and painted on some scales using black.
Finally I used a thin striping brush and an ivy green to paint on the sea weed, a few white dots for bubbles, finish off with a top coat and your done!!