Waterfowl with one leg, especially swans cannot survive on one leg unless human intevention is immediate. The bird will not be able to land, get up or down on banks to sun itself, etc.

If you can, we would suggest that you capture the bird and give it to a wildlife rehabilitation specialist to see if they might be able to provide it with a home and extensive care, i.e., removing if from water throughout the day, etc.

If you cannot capture the bird, then nature will take its course and it will not survive for very long. The Regal Swan