This is an ice circle and it is entirely natural and quite rare. It formed over the weekend on the Sheyenne River about ten miles southwest of Leonard, ND. It is the result of an eddy in the slowly moving river. As the river began to freeze, the eddy froze as a perfect circle. Ice circles are rare because it requires just the right conditions. The river must be at the point of freezing. An eddy must be present. And the current must be slow. If the water is too fast, there is too much turbulence and the eddy is disrupted. If the eddy swirls too slowly, the river just freezes over without the circle.
The movies were made by George Loegering of Casselton, ND.