BAIKAL DZEN/ZEN
The rings are caused by warm, circular currents of water under the ice, called eddies. The eddies' strong currents melt the ice at the edge, but weaker ones keep the centre frozen.
Lake Baikal in Serbia, Russia, is the deepest freshwater lake on earth. Another phenomenon is the quantity of methane gas emissions -- the bubbles make for some stunning photo shoots.
2 January 2021

Baikal Dzen, by Suzette Richards - image generated.