A body of water can only sustain so many bodies!
Having too many waterfowl on a pond can damage the pond's ecosystem, creating unhealthy living conditions. In particular, excessive numbers of ducks can speed bank erosion, as they use their bills to dig in the soft areas around the pond in search of food. Likewise, too many geese can defoliate and trample plants growing along the pond's banks.
Generally speaking, no more than 8-15 ducks or about 4-6 geese per acre (.5 ha) of water is recommended for maintaining a healthy pond ecosystem. This amount allows fish to reproduce in a controlled manner, aquatic plants and mosquito larvae to be kept at bay, and banks to suffer minimal erosion. Having said that, however, there are a variety of factors influencing the "carrying capacity" of a pond, including soil and vegetation type around the pond, whether the birds are on the pond day and night, and more. Each pond needs careful assessment and monitoring to evaluate how many waterfowl will work well in a particular situation.
This lovely pond could use a few waterfowl!
Established ecosystems make for better buffets.
Ducks and geese that live on a pond are dependent on the living things both in and around it. Under the water, they enjoy small fish and their eggs, tadpoles, and mosquito larvae. Ducks will also consume aquatic plants that grow no more than two feet beneath the surface, and geese can eat greens that grow deeper than that. This delicious salad bar will include plants like green algae, duckweed (of course!), wigeon grass, muskgrass, arrowhead, and wild celery.
Around the water, the menu can include small roots, eggs, snails, worms, mollusks, small crustaceans, grass, weeds, algae, aquatic roots, frogs, salamanders, insects, and seeds. Sounds tasty, right? Something else to keep in mind: this kind of diversity will more likely be found on an established, older pond. Newer ponds may need some time to develop their ecosystems before waterfowl are introduced.
They may need a little help to weather the winter.
Don't just leave 'em out in the cold! If you have severe winters, your waterfowl will need a supplemental food source during the coldest months, especially if your pond and the ground around it freeze and remain frozen for many days or weeks at a time.
Predators love "sitting ducks."
Unfortunately, you can expect some losses to predators if your ducks and geese free range on a pond. But you can help reduce the number of losses by providing a lockable shelter for your flock at night. Waterfowl can be trained to go into the shelter by providing them extra feed or treats only at night. They will happily run to the duck-duck-goose house each night to get some tasty morsels from you!