Total internal reflection of light takes place when light travels from a denser medium to a rarer medium and is incident on the interface at an angle higher than the critical angle. The light is reflected back to the denser medium and no refraction of light takes place. Critical angle is the angle of incidence for which the angle of refraction is 900.
Thus, light from the bottom of the water if incident on the air-water interface with an angle greater than the critical angle will be reflected back to the water. For all other angles of incidence light will be refracted to the air.
