Why do objects that are under water look closer than they actually are

Since air has an index of refraction of essentially 1 and water has an index of refraction of 1.33 the angle from which the rays of light reach your eyes is larger than the angle they would in air. This makes the angular size larger to your eyes which makes the object look larger relative to how they would look in air.

(This is straight off google. Dude just google it.)

Objects underwater seem closer to the surface than they actually are because light rays from the object bend away from the normal as they pass from water to air making the objects look closer ... Warm is is less dense than cold air which causes light to bend as it travels through different densities of air.