The illusion is ruthless. A summit drops headfirst into the lake, while sunset clouds appear to continue beneath the shore. This is not a second sky. It is light obeying geometry, provided the water remains calm enough for countless tiny surface patches to send rays toward the viewer in the same organized pattern.
Smoothness does most work. Specular reflection, governed by the law of reflection, preserves the direction of incoming light as each water facet redirects it outward. A ripple does not erase the image; it tilts those facets. When capillary waves are small and sparse, the eye still joins the returned fragments into a coherent upside-down peak. Add wind, and the mirror breaks.
Distance sharpens the deception. At shallow viewing angles, Fresnel reflectance rises, so water returns more of the sky and less of what lies below its surface. Dark water also hides distractions. The lake is not copying the mountains at all; it is briefly becoming a disciplined sheet of glass, with gravity holding the frame.
