Don't believe the cartoons--mirages don't happen solely in the desert. Light bends anytime it passes through air, but when the air temperature varies dramatically over a short distance, causing it to have great fluctuations in density, it can bend light so much that a mirage occurs.

This image is called a superior mirage because it makes the boat look taller than it actually is. And superior mirages always include a portion of the picture that's inverted, as you can see here.