Here's why:
* Total internal reflection occurs when light travels from a denser medium (higher refractive index) to a less dense medium (lower refractive index). This means the light ray must be traveling from water to air, not air to water.
* Critical angle: There's a critical angle for each pair of mediums. If the incident angle exceeds this critical angle, total internal reflection occurs. The critical angle for water to air is approximately 48.6 degrees. Since the incident angle in your scenario is 90 degrees, it's far greater than the critical angle, but the light is traveling from air to water, not the other way around.
In your scenario, the light ray would be refracted (bent) as it enters the water, but not totally reflected. The angle of refraction would be less than 90 degrees, and some light would be transmitted into the water.
