The issue with that is it would create a very large lever arm (not really a lever arm, but it’s the closest way I have to describe it) with the buoyancy force of the neck disappearing unless the neck is placed in the water, and if the giraffe is holding it’s head up higher, the angle necessary to have the neck in the water while the body (the other significant buoyancy provider) is also in the water would dunk even more of the giraffe’s face in the water, almost certainly plunging the giraffe’s nostrils and mouth below the surface.