At first I experienced a glitch where if you didn't move the player to the right right at the get-go, they would be invisible. I figured this out and got to playing the game.
The player moves really slowly, whether up or down, or left and right. I think slightly increasing horizontal player speed, and drastically increasing the vertical player speed might get you a better swimming feel for the player character.
Also, the hit-boxes are rather big and janky, and I ended up hitting enemies that I shouldn't have.
Also, the fact that there's no collecting green fish sound detracts from the experience due to it creating a lack of overall player feedback.
Ultimately, this has the makings of a good game, but needs some ironing out.