Water Mobs

Need help please with Water mobs

I made a crocodile but I can't have him walk in water

I mean, if I use "swim/float when in water" option he just stand on water surface without moving

If I use "swim randomly with speed factor" it does nothing at all.

I have tried everything: checking water mob, unchecking water mobs, and every thing else but my crocodile when in water just stands still

Any idea ?