Why does the transition of light waves from water to air make it seem as if fish and other things in a pond are shallower than they actually are?

Refraction

Explanation:

Light rays reflected from the fish are refracted at the surface of the water, but the eyes and brain trace the light rays back into the water as thought they had not refracted, but traveled away from the fish in a straight line. This effect creates a "virtual" image of the fish that appears at a shallower depth.

so easy. just google the electromagnetic waves and it’ll pop up.