If you're going to be able to use the camera safely when stationary then the lowepro dry zone bags are excellent!
I've worn mine kayaking grade4 :-D
If you want something you can use the camera in, I can highly recommend the aquapac stuff, I've used my dslr at the beach with one of these and it was very very handy!!
Just don't be tempted to open it up before you're back safe & dry!!!