The perspective of the reflection is wrong when done this way. The viewpoint of a real reflection is the same distance below the water surface as the lens is above the water surface in the scene. For instance, imagine a fallen tree in the far distance that is just visible above a rock in the foreground. In a real reflection the fallen tree will be hidden behind the near rock because of the lower perspective. Draw a scene from a side view and trace the light rays to see this graphically.
It's difficult to separate the different parts of the image (foreground, mid and far) to correct this by setting some overlap with distance for the reflection, but it can be done with some detailed work.