Question

Why does an object look bigger in the water

Answer 1

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 the eyes is larger than the angle they would in air. This makes the angular size larger to the eyes which makes the object look larger compared to how they would look in air.

Answer 2

This is your answer for given question:-

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.