Rabbits typically create particles when running, similar to sprinting players. This is glitchy in water because they use the same particles, but with a water texture, so there are animated little squares of water coming out of my rabbits in a water puddle . The particles also use normal gravity, so tiny bits of water are sinking through the water. This is a simple fix, just check if the rabbit is inside a material(water) and then only create particles if it is not in water.

I hope I helped