Mute Swans are an Eurasian species introduced to North America. The swans were released in city parks, estates, and zoos. They are increasing in numbers the wild along the Atlantic coast, the Great Lakes region, and the Pacific Northwest. I have seen them in New England, a few in Minnesota, and a couple of times in South Dakota. This photo was taken in New York at the Storm King Art Center on 11 September 2009.
The problems with Mute Swans include their overgrazing aquatic vegetation and their displacing native waterfowl. Breeding pairs can be fiercely territorial, often attacking people and pets. Programs, including capture or culling, now help control this invasive species (Ciaranca et al. 1997).