Took me a while to work out that this was not just a single flipper, but the whole front end of the animal sticking up out of the water, in which case it can only be a Humpback, due to the white leading edge of the flippers. Possibly with a calf just poking its nose out too.
Haha, thanks Jackie, I can see why you might have thought that initially. This is the only photo I managed to get like that all week, a lucky fluke but still very far off.