Anomalous expansion of water

The anomalous expansion of water is an abnormal property of water whereby it expands instead of contracting when the temperature goes from 4 degree Celsius to 0 degree Celsius, and it becomes less dense. The density is maximum at 4 degree centigrade and decreases below that temperature as shown in graph. The density becomes less and less as it freezes because molecules of water normally form open crystal structures when in solid form.

Due to Anomalous expansion  of water, fish and other aquatic organism can live in winter even if the upper layer is frozen to ice. How?

As temperature of water goes on decreasing in winter, ice of zero degree Celsius gets low density and floats up but water at 4 degree Celsius remain at bottom as it has highest density as shown in graph above. In this way life for fishes and other aquatic animals is possible in glacier lake in winter.