When the amount of organic material in the pool is very high, the available oxygen is used during decomposition for oxidizing the organic compounds; the deep waters and sediment may then become "anoxic", producing conditions toxic to plant life. The smell of hydrogen sulphide when the water or mud is disturbed indicates the presence of rotting organic material. Few animals can live in these pools, and none at all in the worst of the seal wallows which support a population of bacteria and flagellates only.

Interesting lakes are found in continental inland ice-free areas, often called "Dry Valleys" or "oases". Because of the general aridity of the Antarctic, these lakes are often drying up and completely dry lake beds may be found. Dry valley lakes often receive small amounts of melt water carrying salts leached from the rocks, but if the annual input of water only equals or is less than the loss by evaporation or sublimation of ice, the lake will gradually become more saline. Some lakes have water over 13 times more saline than sea water, and freezing points as low as - 48 degrees C.