Dying pond (lake) - a body of water in which freezing events occur continuously (annually) or sporadically. Most often, these are small lakes in which fish die in winter due to lack of oxygen dissolved in the water. Sometimes some lakes are frozen to the bottom. Fish tend, if possible, to leave the frozen reservoir, enter the rivers flowing into the lake, accumulate at the mouths of the rivers and rise to the ice-holes. In small area frozen lakes, in order to save fish, pumping units are installed for the purpose of aeration and catching of fish that came to the water current, special "pits" are arranged.