The reason for a swimming pool to appear less deep than

Solution

The apparent depth will look less that its real depth due to the refraction of light. Refraction is the bending of a wave when it enters a medium where it's speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law.