malformalady:

Pancake ice at the Lummels Pool, Birse, near Aboyne, on a quiet stretch of the River Dee in Aberdeenshire. The pancakes are thought to have formed from foam created by faster flowing water further upstream, accumulating in a corner of a pool. Freezing temperatures last week caused the foam to freeze, and the current bashed them into a circular shape. Normally pancakes form on ocean water or lakes around the Arctic circle where the movement of water keeps the ice from forming a flat sheet. However, they do ooccasionally occur on rivers when temperatures drop low enough.

Photo credit: Jamie Urquhart(link)