As long as you get a very young swan (l year old) that has not bonded with another swan, it is okay to only have one swan. However, it would be better if you could keep the lone swan with other waterfowl such as geese and ducks so that it does have some pals.

The major issue is your local and federal laws as in some areas, swans, especially certain species which are protected under state and federal laws may not be held privately in captive settings without permits. If a permit is required, two swans of opposite gender that may produce offspring may require a breeder's license which will open a lot of other issues such as veterinary exams and costs, habitat size and requirements, etc. The Regal Swan