Here's why:
* Water's unique properties: Water has an unusual property where its solid form (ice) is less dense than its liquid form. This means ice floats on top of water.
* Insulation: The layer of ice on the surface of a lake acts as an insulator, preventing the water below from freezing completely.
* Temperature stratification: The water in a lake stratifies in winter. The coldest water is at the surface (under the ice), while warmer water stays at the bottom. Fish can survive in this warmer layer.
So, even though the air temperature is below freezing, the water below the ice layer remains liquid, allowing fish to survive the winter.