I've rated your game.  Here's my feedback:

- I really like the movement.  It has the right kind of floaty feel to it.  The gravity, acceleration is all nice.  It's fun to simply swim around.  That's a big deal, so well done.

- Graphics are good.  Consider some simple particle effects like bubbles.

- The level design was decent.  

- Don't just use the arrow keys for movement, they sometimes get interpreted as browser actions making the game difficult to play.  Instead also use wasd keys.

- Game really needed music and more sound effects.  Even some underwater ambient sound would have been enough.  Consider spending some spare time building up a library of free music and effects.  Itch has plenty of good stuff.  Categorise it so you waste less time during game jams.  

- Create even a simple menu with options to remove the mobile UI.

- Add some text and images to your game page.  Change the colour scheme to match that of your game's.

You can rate my game, if you'd like.  It'd be most appreciated.