Question

Frozen water (ice) has less density than liquid water.

Answer 1

The ice has less density than liquid water, so it floats on the water surface. Therefore during the winter all the lakes and rivers are frozen only at a top. Deeper layers of water are cold, but still liquid and it allows fish and other organisms to survive. Moreover, the ice cover provides temperature isolation so liquid water beneath the ice has more or less constant temperature (around 4 dgr Celsius)