During mating season or if young are around.
Stay away.
They normally warn you first with a hiss or so.
They do hate dogs, that might not have helped.
scott i do know about swans and geese you know mate, i am a fisherman ***! lol
but where i go there are 3 lakes, with a pair on each lake, the middle lake is where the evil ones nest, and i mean evil, the other 2 pairs are relatively sound!
they come to you for bread, (dog or not) and will hiss at the dog etc! these other 2 are something else!
i will video them so you can see mate!
trust me, there bad!