Why does ice float?

explain why does ice float?

Water has a unique property of anomalous expansion. When water is cooled from room temperature it first contracts in volume and becomes increasingly dense as do other liquids, but at 4° C water reaches its maximum density. On further cooling, it starts expanding and become less dense. This will be continued till the temperature reaches 00C, the point at which it freezes into ice.
This unusual property of water enables marine life to exist in the polar region where the temperature falls below freezing temperature. The outer layer of water becomes ice and floats over the water. As the water has the highest density at 40C sinks down.