Just about everyone has heard of crop circles, but ice circles? A retired engineer this week discovered an enormous circle of ice spinning slowly down North Dakota's Sheyenne River.

George Loegering described the rare phenomenon as "an amazing wonder" and can be heard in the video saying that the perfectly round, alien-like disc measured about 50 feet in diameter.

These ice circles, or ice discs, are believed to be formed by eddy currents, and are found only in slow-moving water. Rotational sheer is a scientific explanation of the event. (Picture a large chunk of surface ice breaking free atop a whirlpool eddy, and venturing downstream.)

While the phenomenon is considered rare, ice discs have been documented several times in recent years, in such locations as England, Russia, and the northern United States.

Most of those, however, were small by comparison.

According to Science Frontiers, a spinning ice disc with a diameter of 160 feet was discovered in Sweden's Pite River in 1987.

The publication stated: "The fringe literature has made much of the huge, slowly spinning discs of ice seen on some rivers in northern climes. UFOs are connected somehow. Or, more recently, they must be associated with the infamous crop circles!"

Presumably, there is no UFO connection to ice circles. But they're pretty.