Only aggression I have ever witnessed was by a cotton mouth here in South Georgia, USA. I was paddling with a GP painted with a red and black diamond pattern. The snake was really irritated by my paddle and chased me down to strike at it. As a test I again paddled past him with my unpainted storm paddle and he didnt care a bit.

Canada Geese are often aggressive. They used to crowd round my water-loving labrador at the local lake during nesting season, forcing her to head for the bank, even tried to mob me and my kayak. One took over the patio at my workplace cafeteria for her nest stopping the weekly BBQ, and last year I watched a bunch of them chase off a few ducks at the lake in Stratford Ontario, then four swans did the same to the geese. It was a skilful job of herding.

Stratford has resident swans that are kept indoors over the Winter and released every Spring - it's quite a show

http://www.youtube.com/watch?v=2wn_jOPhAO4