Land, sky, and water.
Land - It looks like a default texture in a 3-D rendering program. It seems to have no real shading (just light or shadow) and no detail, which is unusual for a real photo.
Sky - They clouds look too sharp - not diffuse enough. I think they also show too much of a dynamic range for being so patchy (they get too dark closer to the horizon). Also, it seems as though the Sun is directly overhead (judging by the bright patch in the clouds), which is in conflict with where the shadows are on the land.
Water - It looks way too reflective, and the ripples in the foreground look too large - there is no small-scale structure in them.
Also, overall, there's no haze. In almost any landscape shot that shows significant depth, there should be haze the farther away an object is.
Now if you come back and say it's real, I'm going to feel like a moron, but that's just what it seems like to me.