I just had a video pop up on my computer of a super cool winter phenomenon that happened in Maine. It is called an ice circle or an ice disc - and that pretty much explains what it is. These form on rivers and look extremely cool and have been referred to as ice crop circles because they are so perfect and almost unnatural looking! The recent one from Maine looks almost like a full moon...but on the ground. Check it out.

I've never seen an ice circle in person before but I do remember hearing about them happening here in Idaho. I was able to find a few videos of them in Salmon and in Eastern Idaho near Yellowstone.

Here's the one from a few years ago on the Salmon.