What is a whirlpool? Whirlpool appears like?

The river water is running fast, when it comes to the abutment, it is blocked, so it has to step back. But the back is a stream of water flowing in, pulling it along. Thus, the number of these countries could not advance, nor back, had to run the circle near the bridge. So there is a whirlpool there.

In places where the river swirls, it is also easy to create whirlpools.

On the river, around the wooden piles or rocky outcrops rising from the water can also appear swirling. That's because the water flow after being stopped by obstacles, it can only go around to the sides. When it comes to the back of the obstacle, because it is in a river where the water flows slowly, affecting the flow of the water, so it rushes into the water that prevents its flow and causes it to run.

In places where the river swirls, it is also easy to create whirlpools. Since river water tends to flow in a straight line, so near the face in the loop, the water flow has 'escaped' the river bank to flow straight. However, the flow of water outside forced the flow of water inside to go around. When the surface water flow is subjected to the pressure of the outside surface, the part of it will flow additionally into the place of dehydration, and thus form a whirlpool.

If you notice, you can see that the whirlpool on the river appears in places where the speed and direction of the flow suddenly changes.