Amictic lake
Amictic lakes are "perennially sealed off by ice from most of the annual seasonal variations in temperature." Amictic lakes exhibit inverse cold water stratification whereby water temperature increases with depth below the ice surface 0 °C (less-dense) up to a theoretical maximum of 4 °C (at which the density of water is highest).
Hutchinson–Löffler (1956) classified amictic and other types of lakes based on physical/thermal processes. These processes are influenced by solar radiation and wind. They are strongly tied with seasonality and thus associated with latitude and altitude. Amictic lakes occur in Arctic, Antarctic, and alpine regions and due to permanent ice-cover, these physical/thermal influences have a limited effect on circulation in the water column. For this reason, amictic lakes are commonly referred to as lakes that never mix.