Water or Sky?

A Classic Backblip

EDIT:
It is all sky! I couldn't resist this one. We were travelling home with the sunset behind us and I asked Mr G to please stop so that I could Blip this beautiful sky. I actually didn't get out the car but put my head through the sunroof! I cropped the horizon of mountain tops so that I could keep you guessing. Well done to those that spotted the birds.