One of the specificities of water, compared to almost all other liquids, is that its maximum density is not reached at its fusion point but at 39.1° F (3.98° C). Thus, in a deep lake like Lake Servières, where the water layers are stacked by density, the bottom temperature is always 39.1° F (3.98° C). In winter, the water at 32° F (0° C), less dense, rises to the surface and freezes, forming an ice cover. Conversely, in summer, the less dense upper layers are warmer than the bottom, whose temperature is 39.1° F (3.98° C). This phenomenon allows the lake's fauna to benefit from an always liquid zone at the bottom of the lake, with constant temperature throughout the year.