The direction of a light ray changes when it goes from one medium to another, for example from air to water. This phenomenon is known as refraction.

A translucid object can then alter the trajectory of a light ray.

For example light rays going through the edge of a circular surface of water converge. This is why you can burn a piece a paper with a bottle of water and the light of the sun. This also explains why an object seen through a glass of water can appear reversed.

The enveloppe of rays going out of the water is curved but all rays are made of three linear parts: you can see this by hovering your mouse over them.
You can also check what happens when you replace water with another material.