When you swim on the surface of a chunk of water terrain covered by a non-CanCollide part, the character acts strangely. Its sort of like you can collide with the part for a split second.
Plain water:
This is completely normal. The problem comes into play when swimming in the chunk covered by the part:
It isn’t very obvious, but it’s possible to tell that the character bounces a little at certain points.
These are the part’s properties. CanCollide is set to false:
I’m not sure what’s causing this problem or if there even is a fix. I first noticed this when I was experimenting with collision groups.
To reproduce this you simply fill an area with water and adding a part (CanCollide = false) over it, or you can download the place file and simply try this for yourself:
WaterBug.rbxl (17.5 KB)