Why don lakes and rivers freeze solid?
If they’re small enough, they will. However, any lake or river of sufficient size will not freeze solid. The reason most lakes and rivers don’t freeze solid is because water, ice, and snow are good insulators and poor conductors of heat. The portions of a lake or river that are exposed to the cold winter air will freeze into ice and this ice insulates the water below from further rapid freezing. Also contributing to the prevention of bodies of water freezing solid is an interesting characteristic of water. Like most other forms of matter, water become denser as it cools, but beginning at about 39°F (4°C) something odd happens – water begins to lose density as it gets colder, becoming least dense when it freezes into ice. This is why ice floats. As water becomes colder it rises to the top, eventually freezing to the layers of ice that are already there. Insulation of the water beneath is increased as the ice thickens so cooling of the water beneath slows. Many lakes will eventually free
