The color of the ice layer covering a lake is a useful, although insufficient, indicator of its stability and thickness. It is thus possible to estimate that a light gray to dark black or speckled ice is melting and that its density would not necessarily resist the weight of a passer-by. White to opaque, the ice layer consists of snow saturated with water and presents a significant and dangerous porosity caused by air pockets. It is only when it is blue, more or less clear, that ice is sufficiently consistent, dense, and resistant, provided its thickness exceeds 3.93 in (10 cm).