Nice game, here are my feedback on it:
+ The controls under the water are really neat, I felt well the rapidity and the agility of the character, it was a good feeling!
+/- I liked a lot the art direction/universe, however, it is too bad that there are some elements which are too pixelated.
+/- I found nice the variety of the dangers, but I died too many times, it was a bit hard for my taste.
+/- The music doesn't loop well, especially the first one, we can hear when it restarts, otherwise in general the music is nice.
Overall: Cool work!