Anomalous expansion of water is blessing for living organisms in water''. Explain this statement.

Explanation

Anomalous expansion of water :
Thermal expansion of water is non uniform with temperature.
It contracts on heating between `0^(@)C` and `4^(@)C`. The volume of a given amount of water decreases as it is cooled from room temperature, until its temperature reaches `4^(@)C`.
Below `4^(@)C`, the volume increases, and therefore the density decreases.
This means that water has a maximum density at `4^(@)C`.

This property has an important environmental effect : Bodies of water, such as lakes and ponds, freeze at the top first.
As a lake cools toward `4^(@)C`, water near the surface loses energy to the atmosphere, becomes denser, and sinks, the warmer, less dense water near the bottom rises. However, once the colder water on top reaches temperature below `4^(@)C`, it becomes less dense and remains at the surface, where it freezes.
If water did not have this property, lakes and ponds would freeze from the bottom up, which would destroy much of their animal and plant life.