The common name for the layer of ice that forms in water is called "ice cover" or simply "ice." This layer typically forms when temperatures drop below freezing, causing the surface of lakes, rivers, and oceans to freeze. Ice cover can vary in thickness depending on the environmental conditions and duration of low temperatures. In polar and subpolar regions, ice cover plays a critical role in regulating temperature and affecting local ecosystems. Additionally, its formation influences weather patterns and is crucial for species that rely on ice-covered habitats for breeding and feeding.