What is an ice circle?

If you've ever come across a big, circular piece of ice rotating in the water, chances are you encountered an ice circle.

An ice circle "is a thin slab of ice that rotates slowly. It's a rare natural phenomenon that occurs in cold climates and areas with slow-moving water," according to AccuWeather.

Ice circles usually form on the outer parts of rivers because of rotational sheer, AccuWeather said. This force breaks the ice off and twists it around, creating the ice's rotational movement.