Good job! It was something new, I liked the idea and I enjoyed. I am not sure how much is fitting the theme of the jam though. 

It is not convincing me the idea of having to press both Spacebar and Enter at the same time for bouncing on top of the enemies. This is something you could maybe polish (only pressing space, automatic bouncing...not sure). Also you could do some hp bar for the player and that it is possible to do some little jumps on the land (like the fishes do).

This was surprisingly addictive and a lot of fun to play. One thing I would note is that maybe the controls for the game should be listed in the game page or ideally, before you get to play the game. I found myself stuck a lot on the first bit because the movement was so fast and I didn't know about how to use ENTER until I made the jump. Having an "about" button or screen before you move could really help. But besides from that good job and well done :)