This was incredible!
You created a cool atmosphere both on the ground and underwater. Your sound design increases a lot the atmosphere you bult. Your mechanics are so unique. I love the mech design. This game reminded me a lot to Mario Sunshine, I'm sure these mechanics have a lot of potential that hasn't been explored in general. The map is designed and looks great!
Maybe the game feels a bit slow, the idea of releasing a button to jump doesn't always work and makes the experience slower if you don't get it at the first time. More sounds could be great to improve the communication with the player. For example, the first time I didn't notice that the water tank was the sphere on the bottom left of the screen, so maybe an indicator would be good. Once the game starts, you should give the player some time to process what's happening, maybe a title screen or a short message of what you have to do could be good ideas.
This game idea is great, so I'd like to see if you're gonna do more with it. It may work for a full game in the future!