A retired engineer out hunting in North Dakota on Saturday spotted a huge circle of ice spinning on the Sheyenne River, over 50 feet in diameter.

George Loegering posted video online on Tuesday of his unusual sighting, clearly showing the snow-covered disc rotating.

“We are looking at the Sheyenne River here, down at the Owego property. Just west of the bridge is a perfect circle of ice probably close to 50 feet in diameter spinning in the river. It’s an amazing wonder. Don’t have a clue how it did it, but that thing is rotating, as you can see,” Loegering is heard saying in the clip.

Loegering, who lives in rural Casselton, about 20 miles west of Fargo, calculated the disk’s diameter to be about 55 feet, took photos and videos of it and then turned to the Internet for more information about what he, his brother-in-law and nephew had seen.

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Allen Schlag, a National Weather Service hydrologist in Bismarck, and Greg Gust, a weather service meteorologist in Grand Forks, said a combination of cold, dense air last weekend and an eddy in the river likely caused the disk.

The cold, dense air – the air pressure in Saturday in nearby Fargo was a record high for the city for the month of November, according to Gust – turned the river water into ice, but since the water was relatively warm it didn’t happen all at once.

Floating bits of ice got caught in the eddy and started to spin in a circle.