What is created behind a rock or obstruction that flows in a circular upstream direction?

The phenomenon created behind a rock or obstruction that flows in a circular upstream direction is known as eddies.

Eddies form when a fluid, such as water, encounters an obstacle, causing the flow to separate and create a rotational motion in the nearby water. This rotational flow results in a circular pattern that can often be seen swirling around behind the obstruction. Eddies are commonly found in rivers and streams, particularly where there are rocks or other structures that disrupt the current.

In contrast, whirlpools are typically characterized by a more intense and localized downward motion of water, often occurring in deeper or more confined spaces, whereas eddies are broader and less intense. Discharge refers to the volume of water flowing through a given point in a channel over time, which does not directly relate to the circular flow created by eddies. Currents refer to the general flow of water in a specific direction and do not capture the circular motion occurring specifically behind an obstruction.