Muscovies are more like geese than like other ducks in that they can largely subsist on grazing, whether on grass or on aquatic plants. Your pond could definitely benefit from a small flock of either, provided a few things....what will they eat if they finish off most of the pond weeds....is there a grassy area nearby to graze them on? What will you do with them in the winter when the pond is frozen and there isn't anything growing for them to eat....most wild ducks and geese simply leave. They will need some sort of
shelter and food for at least three or four months. If you start out with one pair and they successfully pull off a hatch of eggs, you'll have a bunch by the next year, possibly all you need, and then you can start eating eggs or birds...