There were a handful of swans swimming through the freshwater ponds at Ellis Creek Water Recycling Facility in Petaluma, CA. This particular swan was quite agitated that a Canada Goose was also swimming around its pond, and continually swam after the goose until it decided to leave.
Later on I understood its unhappiness with the other bird around, since when I walked around the backside of the pond that was overgrown with rush, I saw another swan sitting on what I guessed to be her nest.
Even though this is an introduced species in America, they are still quite fun to see, as they truly are a beautiful species.