This is Janusz Pond a few years ago. It borders the Polesian National Park in Western #Polesia. A few ponds like Janusz were included in the park on its formation in 1990 and they look much wilder.
On closer look the spots turn out to be dead swan mussels (Anodonta cygnea), a species found only in very clean water.
@szescstopni are they edible?
@RoboticistDuck They're used as animal feed, I'd have to check on use by humans. Probably not very tasty .
Those mussels are some of the largest freshwater mussels, reaching 20 cm in length. The pocket knife placed for comparison is 9 cm long.