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.

Ice circles are thin and circular slabs of ice that rotate slowly in the water. Ice discs have most frequently been observed in Scandinavia and North America, but they are occasionally recorded as far south as England and Wales.

An ice disc was observed in Wales in December 2008 and another was reported in England in January 2009. An ice disc was observed on the Sheyenne River in North Dakota in December 2013.

An ice circle of approximately 50 ft. in diameter was observed and photographed in Lake Katrine, New York, on the Esopus Creek around Jan. 23, 2014. In Idaho, extreme weather led to a rare sighting of an Ice disk on the Snake River on Jan. 22, 2014.
An unusual natural phenomenon, ice disks occur in slow moving water in cold climates and can vary in size, with circles more than 15 metres (49 ft) in diameter observed.