They look too perfect to be natural—large circles of ice slowly spinning in rivers.

Video captured in 2016 shows a seemingly symetrical circle of ice in a river near Omsk Oblast, a region in central Russia that sits just north of Kazakhstan. At first glance, the ice seems to be barely moving at all, but closer looks reveal a slow, steady spin. Even more bizarre is the seemingly perfect symmetry of the disk.

According to the filmmaker (who did not provide their name), the spinning circle of ice measured an estimated 50 feet in diameter.

While the Russian ice circle is rare for its large size, the phenomenon isn't quite as unusual as it might seem. Ice disks have been filmed in