To add to what Rainman said, even if they are Triploid Carp, if they denuded the bottom completely of plants, then they will root around in the bottom looking for something to eat. In one clients pond they are rooting around to eat whatever cattail roots they can and sometimes will break off young cattail shoots. The pond owner reported a cattail plant moving across the pond like a periscope of a submarine. One guess who the culprit was.
I forgot to ask, what kind of ducks do you have, and how many are there?