Ice is less dense than liquid water because of ice’s structure that spaces the water molecules further apart. Because of this, ice freezes over water, and leaves liquid water beneath the ice layer.

Ice is less dense than liquid water. This is a property of water that makes it special:

In liquid water, the molecules are not in a definite shape. They are all over the place. However, in ice, the water molecules are spaced out, with more distance between the water molecules than in liquid water, effectively making ice less dense than water. This explains why ice cubes float in a glass of water.

The fact that ice is less dense than liquid water is important in cold climates, because it causes ice to freeze over large bodies of water, rather than freezing the entire body of water.

Take ice fishing, for example. When a lake freezes over in winter, only the top layer of water is frozen. If you ice fish on a frozen lake, the only reason you can ice fish is because there is still liquid water underneath the top layer of ice, as ice is less dense than liquid water. That way, aquatic organisms can still survive underwater despite how the top layer of the lake or body of water has frozen.

In cold climates, this not only allows the aquatic organisms to continue to live in the body of water, but also can be useful to terrestrial organisms as they can cross these frozen lakes and ponds due to the top layer of ice.

it also preserves a way for predators that prey on aquatic organisms to continue to get their source of food, if said predator does not hibernate.