When you wear a pool Tube and enter a water volume your physics change however you don’t float to the surface so you keep sinking to the bottom.
Steps to Reproduce
Create a water volume and wear a pool tube, then jump in.
What I expected to happen
To float on the water surface.
What happened
You maintain your downwards momentum and do not surface.
Notes / Media
If you run into slopes you can change your height, there is no gravity so you end up locked at the height you stop touching them.