Just wanted to notify you that the issue is fixed now! Sorry that it took so long.
Recent community posts
First of all thank you for trying out my game. To swim up you have to push [Space] repeatedly. Basically the swim mechanic is like the fly mechanic of Flappy Bird (One single press is a little boost upwards. To really gain height you have to press kinda fast).
If you have tried this and it still isn't working please contact me again, as this is behavior that neither me nor any of the testers experienced.