Clarification: "Water Currents"

I think its a shadow cast by the waves/ripples on the surface.

well, not really a "shadow", but as light enters water, it bends
(unless the light is entering perpendicular to teh surface)
And if you have waves on the surface, the light is being bent
at different angles, so there will be points under the water that
get more light because more light is bent to that location.

If I were describing it in a fiction, I'd probably say something like
"the water rippled, casting shadows on the wall"
or something.

If its non fiction, I have no clue if there's a term for this.

There are several different things at work here, with the light.

One is reflection - that would be the light reflected off the surface of the water onto the sides of a pool or aquarium above the water. Since some of the light is being reflected off the surface, it's dimmer underwater than above.

The second is refraction. That's what happens when light passed through a medium (like a prism) and is bent. This happens when the light enters the water and the angle at which it's striking changes at that interface so it goes off to one side.

Like Greg said, because the waves at the surface are curved, with convex areas and concave areas, refraction is not consistent across the whole area of the water. The light gets focused on some areas and diffused away from others so you get bright lines and darker, shadowed lines. They tend to make lines because the crest (and trough) of a wave forms a line.

You could talk about the refracted light rippling on the bottom and sides, or describe the constantly moving light focusing and refocusing because of the restless waves. But, I wouldn't call it a "current" because currents are flows of water, like the current of a river that runs down to the ocean or the Gulf Current, that flows north up the east coast of the US. What you're talking about is the result of wave action, not current.

I'm not sure what the obscure scientific terms would be--haven't done any physics since about 1972.