I used a pool liner to line the pond, so the mud comes directly from the duck's bill. Ducks need the mud to eat, but also the water, and as you can guess with a bill, most of that very fine powder dirt goes into the pond.
Unfortunately, the pump needs to be under the water level, I can't dig a hole and path for the tubes w/o risking the side collapsing. So opening it to clean it is a real chore, it's also fenced so even more annoying. Plants with ducks is also impossible, they eat everything...
I'll get a pic up later today.