Given reasons
(i) Lakes freeze form top towards bottom.
(ii) Ice floats on water.

Explanation

Density of ice is less than that of liquid water. During severe winter, the temperature lake water keeps on decreasing. Since,cold water is heavir, therefore, it moves towards bottom of the lake and warm water form the bottom moves towards surface. This process contionues. The density of water is maximum at 277K.
Therefore, any futher decrease in temperature of the surface water will decrease in density. The temperature of surface water keeps on decreasing and ultimately if freezes.
Thhus, the ice layer at lower temperature floats over the water below it . Due to this, freezing of water into ice takes place continuously from top towards bottom.
(ii) density of ice is less than that of liquied water,so if floats over water.