The diving action (spacebar) feels more like a booster than a dive since you can move up and down using WASD. It feels a tad unnecessary even more since the diver becomes unresponsive/too fast after the 'dive'. Only managed to get 179m :(
Just a suggestion but you can make it more fun by maybe only having a left/right button and a dive button. Pressing the dive button could give the player momentum to dive by consuming a small part of oxygen. The momentum could fade with time thus the player needs to constantly 'dive' as they go deeper.
It was fun nevertheless :D