(I am now in a rush to test as many games as possible to help, so please do not mind the cursory reviewing style.)

Semi-on-the-fly remarks:

1. (Seeing "für" in the tagline, are you from a German-speaking country or even German, by any chance? :))
2. [testing the desktop version, in accordance with the game page]
3. Wow, cool in-game music! :D (the music from the menu was also nice, but less groovy) Volume is a bit loud (but I understand volume features and such utility can take away some precious creation time).
4. The first indication disappears a bit fast; it takes some time seeing where things are, and the hero appears in the middle of it.
5. Controls are QWERTY-only instead of layout-independent (I have an AZERTY keyboard), BUT arrow keys are enabled.
6. Great sound effects (interacting, bin that even opens).
7. Bubble effects… A lot of details. By the way, I notice the general distortion effect; I have also used it in a (yet-to-be-completed!) submarine game, it really gives life easily to the scene. :) Did you use a shader? (I notice there is a small horizontal ‘corruption’ on the left-hand and right-hand sides of the screen, and I remember from writing the distortion shader that this can happen. ;))
8. I would have liked a pause feature (I write as I play!!) and one to go back to the menu / start again, but this is a nitpicky detail. :p
9. Possible bug: going back to the menu (after a game over) does not switch the music back to menu music.
10. Helping those little creatures is too cute! :) I really liked the context and cuteness right from the game page description. :)
11. Ah, the sound effect for putting garbage in the trash reminds me heavily of the breathing sound from the subgame ‘Spelunking’, which is also underwater, from "The Time Warp of Dr. Brain". :)
12. You can continue playing during a game over; perhaps this is expected.
13. The gameover banner says how much garbage you removed; is there some objective? I think it could be interesting to set one or several thresholds and have different ‘endings’ depending on your result. :) Also, keeping track of the player’s high score could be interesting.
14. Oh, did not try cutting the music! X) Oh, BUG: pressing Space toggles the music on and off once you have clicked on the loudspeaker logo! :o I guess the focus is on it. Luckily, the E key does not have this problem.
15. Another funny detail: if you hold a piece of garbage while freeing a creature, the diver puts it in his mouth. X) :)
16. I notice there is a very sweet feel to the game, even in saying that having no dioxygen means the diver goes to the surface, not that he dies. Very peaceful vibe. :)
17. Depending on the efficiency of the creatures, I guess the best strategy is to free some amount (possibly all, which I did), and then bring back garbage yourself.
18. A fish gets a bit stuck (rapidly turning left and right) on the upper-left of the anchor; but gets away then. I have not checked the AI in detail, but the friendly creatures seem to behave coherently.
19. Small graphic ‘bug’/incoherence: if you catch a falling can, because of the animation delay between pressing and actually grabbing, the can has time to go way below and then ‘teleports’ itself to your hand. ;)
20. After game over, the counter still goes up when the creatures (or you) bring back garbage. (I managed reaching 68 legitimately.)
21. Oh, I see a turtle at the upper right, stuck against the wall, stuck turning quickly left and right!! :o Collision bug, probably.
22. One final note: I like the parallax background and hand-drawn graphics (both scenery and entities). Rather cute.

Takeaway: clearly presented game — although I would have let a bit more time to read the instructions or asked the player to press a key to let it sink in (pun unintended XD) —, with a very sweet atmosphere and context. The visuals and sound effects are very readable. I also think the game connects very well with the theme, and is rather original.

The criticism I would make regards gameplay: I think the game somewhat lacks a precise target (the threshold(s) idea I suggested could be a solution), and possibly some other mechanics, because otherwise, freeing the creatures and then collecting garbage is rather straightforward. One suggestion: allow the creatures to get trapped again in some garbage/nets/plastic that gets thrown in the water, so we have to free them again! :) So, these limits could rather easily be solved through some extensions.

Thank you for the sweetness! :) Those fishy turtly figures and groovy music will possibly haunt my night. XD

PS: oh yes, maybe some additional sounds would be beneficial, such as when freeing a creature, or when some garbage is thrown in the water.

PPS: I see Skyptm (whose game I tested just before yours, by sheer coincidence!) already suggested the same garbage-trapping idea as me. X)

I love the homemade style indie graphics and rocking sound track. I also detected some sort of water filter for the background? That was cool. I do think an obstacle of some sort would add to the overall gameplay and objective something like.... sharks!  :)