Wow, thanks for doing the video! And yes I really decided to make this lite experimental kinda game to play with that idea I had for controls. If I decided to expand on this idea at some point I think your right, some plankton to eat would be cool, and maybe those boats you see on the surface could even be whaling boats which would try harpoon you, I would also like to vary the depth of the water far more.
I am kinda surprised how confused everyone gets when they try it, the controls actually work in the same way as most dogfight games, ie you don't stay aligned to a vertical axes but instead have to roll to one side and use vertical input to make a sharp turn, this is kinda confusing, but every other flying game manages it, so I figured it was worth it to give people freedom to do barral-roles through water etc.
Moving the mouse up and down moves the wales tail up and down, this does two things, like in real life the airfoil effect of the tail while its sweeping up and down creates a forward force. The other thing that happens is while your body is curved in a direction you will turn following that curve.
I expected some of that to be confusing to people but a recurring thing everyone keeps doing is turning the opposite way they want to go, I have no idea why this is, the mouse input is set up so that you literally move the mouse the way you want to go, if you veering sharply towards the ground, you need to start moving your mouse away from wherever the ground is! however I think the speed of the whales movements and the fact you have to flap the tail to move throws people somehow which is really interesting. Also, speed is fine, just as long as you know how to drive, I'll upload a video at some point, I think this experement has kindof failed the intuitiveness test but it is one of those unusual things that looks and feels better the more you get your head around the controls I think.