You said that the light bounces off the surface of the lake. That would be reflection. Really the mirage is refraction. The lake cools the air immediately above the water. If you stand above the cool air, in the warm air of summer, the light bends downward as it passes into the lower, cooler, denser air. That bend lets the light pass over the horizon. My mother’s cottage sits 10 feet above the water line, so it is above the lake-cooled air. The Charity Islands were not over the horizon, but the mirage made them appear to float above the water line. I don’t know why the mirage cuts off the bottom part of the image; maybe I should do the math.

Hmm, your blog would benefit from a “Preview” button, so that I could check whether I typed the HTML link correctly.