Underwater, objects may appear how much percent closer than they would in the air?

Underwater, objects can appear to be about 33% (often rounded to roughly 35% for practical calculations) closer than they actually are in air due to the refraction of light as it passes from water to air. This phenomenon occurs because light travels at different speeds in different mediums, leading to a bending effect.

When light moves from the denser medium of water to the less dense medium of air, it changes direction, making objects appear to be at a different position than they actually are. This is a crucial concept for divers to understand, as it impacts navigation, distance perception, and safety underwater. Recognizing this visual distortion allows divers to properly judge distances and avoid potential hazards while exploring underwater environments.