Swans are some vicious assholes. This dog was just swimming minding it's business when the swan started thrashing it with its wings:
More vids of swans:
And of course, swans vs. geese. According to the creator of this video:
The first half of the video is amusing in its own right - two parents honking at their gosling to jump over a small gap, which it is unable/unwilling to do. Possibly due to all their racket, a nearby swan that considered itself the king of this lake swam up to start a fight.