system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does swirling water cast a shadow?

Like in my pool, while the pump is running, I can clearly see the bottom, but the swirls from the jets create shadows on the bottom of the pool.
gpt
It is due to refraction. The surface of the water is not flat in this situation. It makes a lens that bends some of the light. The shaded part looks darker because the light that would hit it is bent and hitting some other part of the pool.

In other words the lens made out of the surface of the water is bending light away from the shadow.