what can I do?

[RugenerGooser]

For a pond, your poop eaters are bottom feeders like catfish. The poop falls to the bottom and catfish require less oxygen to survive than other fish. They eat waste and any fish remains that result(scavenging). You have your waterfowl and duckweed on the top, your other fish in the middle and your catfish on and near the bottom.

 

[8GeeseALaying]

If you get catfish, beware of letting goslings or ducklings in the pond. The right sized catfish can and will eat them. Just because they are bottom feeders doesnt mean they wont eat at the top or just eat waste. I have fished for years and have caught catfish at different levels with different types of bait. Also witnessed wild ducklings and canadian goslings get gulped off the surface of the water. Bass will eat them too. If they are predator fish and can get their mouth around it they will eat it.

 

[kimberly35042]

You would almost certainly have to have a filter system. If you only have a few geese, the black plastic masonry pans and easy to dump out each day and clean.