I did not like the game that much, however, there are few cool things that I'd like to address:
The waves work pretty well, I don't know how you did them, but I'm impressed at how consistent they are.
The whole movement is really cool! If you'd play around with it a little bit more (and maaaaaybe cut off the whole "picking up garbage" thing and make it a stunt game) this could be one of my favorite games.
For my money, the things you could improve on the movement are the following:
Gravity: Right now, you programmed your fish to have movement turned off in the air, and on under water. Introducing gravity will be hard with this, but right now, when the fish is in the air, it is falling at a constant speed, which is very very slow (I'll come back to this) and feels unnatural. If you did something like adding gravity (which is then turned off or even better, faded from 1 to 0 when you go back to the water, it would be a lot more smooth!
Movement: Overall, the movement is cool, but it feels really slow. If you take a reference from flying fishes, they are a lot faster than this. But maybe adding something like a temporary sprint mechanic would make up for it.
Usually I don't give a lot of "improvement" feedback but your movement really struck me, I like it a lot! Thanks for the experience!