The San Francisco prankster group The Cacophony Society has for years been running against the Bay to Breakers run dressed as salmons.
Now RKCR/Y&R in London has come up with a completely unique concept of having people dressed as salmons run against a race in New York. OK, I was sarcastic. They have stolen the whole thing, including twists like one salmon ending up in a bar, available via YouTube.
And to give credit where credit is due (as opposed to RKCR) I found this story on Laughing Squid. Go there for the full story and all the links.