Does ice float on water? Why is that?

Yes, ice floats on the liquid water because the solid form of water has a lower density than liquid water.

Why? It's simple! Because the geometry of the hydrogen bridges, which are forming only at lower temperatures.

For almost all substances and all other 11 unusual  forms of water,except ice-XI, the solid state is denser than the liquid one. Fresh water is most dense at 4 ° C, and it will sink by convection as it will cool to that temperature and if it's cooled further, it will rise.

Because of this property, depth water will be warmer than  surface ice water. According to this, the ice will be formed from the surface and it will extend down and most of the water underneath will remain constant at 4 ° C. The survival of animal species is due to the fact that the bottom of a lake, sea or ocean is virtually isolated from the cold.

Almost all other chemicals are denser in solid state and they are freezing from bottom to top.