I have a very sweet Speckled Sussex rooster and 16 hens (most of them very tame). I also have a Cayuga drake and Khaki Campbell-Cayuga duck. The drake and chickens were adults when I received them, which was at the same time.
The ducks do not like the chickens. The drake chases, pokes, and sometimes pulls feathers out of the chickens. The duck just pokes them. The chickens walk around on eggshells around them. After a couple of months of watching unhappy ducks and nervous chickens, I decided to separated them.
The ducks did splash water around inside the coop, but their animosity towards the chickens is the main reason why they now are living in the guest bathroom!
It would have been okay if I had left the ducks with the chickens, but ever since the ducks moved inside, they have become very affectionate. They don't like to be petted, but they like to cuddle (under their own terms).