CNN - An amazing phenomenon is blowing minds in Maine.
A nearly-perfect spinning disc of ice formed in the Presumpscot River in Westbrook.
The disc is roughly 100 yards in diameter and is spinning in a counter-clockwise direction, according to a city official.
Experts say discs can form in a slow-moving, rotating part of a river. Slow-moving water freezes faster, forming a circle of ice.
It's a natural but rare phenomenon.