Cool entry! You did very similar to what we were attempting to do, but in 2d instead. We ended up with a little sea exploration project but the original intention was to dive deeper and deeper into the ocean finding more and more cool and hidden treasures.
The concept of continuing to go deeper as you progress is really cool. Would have been cool if you took the surface water away after level 1 and put a little cave top above it or something similar to show deeper. Cool idea!