I have had ducks this year. I am told they can cause algae issues because of their "duck waste". My pond is pretty large 5000-6000 gallons so I wasn't too concerned about that. But then they started crushing my bog plants from sitting on them, sitting on my floating planters crushing those plants and eating the rest and then knocking rocks off the falls into the deep part of the pond 40" deep.
I was not happy.
Every time they showed up I would get out there and try to chase them off but they would just swim to the other side of the pond mocking me LOL. My husband said I looked like a crazy woman out there running around the pond screaming, I probably did LOL. But then I taught my chihuahua to be a good bird dog LOL. He didn't care about the ducks until one day I was standing in the water cleaning the pump off while the ducks where in there and that really pissed my little guy off. It was no big deal until his momma was in the water with the ducks, then his internal bird dog all the sudden emerged. He went crazy running around the pond trying to get those darn ducks away from his momma until the flew away. I told him what a good dog he was and gave him a treat. Now he guards the pond for ducks and if they show up he runs them off. They don't show up anymore. LOL