There are crop circles (you won't find them in Bluffton), and ice circles (and now you will find them in Bluffton).
Look closely at this photo.
It shows ice circles on the Riley. Brennan Davies noticed them on the Riley near Kimmit's Hill. (That's the bluff along Riley Street near Garmatter Street, for anyone under 40.) He learned about the on the Weather Channel.
Here's a definition from the Internet:
An ice disc, ice circle, or ice pan is a natural phenomenon that occurs in slow moving water in cold climates.