Why lake says frozen on top and liquid under?

Lakes freeze on the surface due to the lower temperature of air in winter, causing the water at the top to cool and solidify. Ice is less dense than liquid water, allowing it to float, which insulates the water below and prevents it from freezing. As a result, the deeper layers of the lake remain liquid, maintaining a habitat for aquatic life even in cold conditions. This stratification is essential for the ecosystem, as it helps preserve a stable environment beneath the ice.