Why does ice float on the surface of water?

Ice floats on water because it is less dense than liquid water. When water freezes, its molecules arrange themselves in a fixed crystal structure with spaces between them. This structure occupies more volume and reduces the density of ice.

Since substances with lower density float on substances with higher density, ice floats on the surface of water. This property is very important for aquatic life because lakes and ponds freeze only at the surface while water below remains liquid, allowing fish and other organisms to survive.