Aliens don't seem to be slowed down by water, nor do they give off the swimming effect. Is this supposed to be like this? Because I think it might be better if the aliens don't just breeze through the water so easily.

There are currently no easy or performant ways to control how fast biters are on water. Also I only do the effects for players since it might be a bit too much (and also performance intense) if I do it for all entities.

I do kinda like that the biters are speedy and the player slow in water ... making water a death trap ;)

Okay, so it's not a bug.

I do feel however, that there should be a way to limit how fast they move. Especially in deep water. I don't mind them crossing it, but I'd personally love to be 'my island is a fortress'.