Anoxic waters are areas of sea water or fresh water that are depleted of dissolved oxygen. This condition is generally found in areas that have restricted water exchange.
In most cases, oxygen is prevented from reaching the deeper levels by a physical barrier (silt) as well as by a pronounced density stratification, in which, for instance, heavier hypersaline waters rest at the bottom of a basin. Anoxic conditions will occur if the rate of oxidation of organic matter by bacteria is greater than the supply of dissolved oxygen.
Anoxic waters are a natural phenomenon, and have occurred throughout geological history. Anoxic basins exist at present, for example, in the Baltic Sea, and elsewhere (see below). Recently, there have been some indications that eutrophication has increased the extent of the anoxic areas in areas including the Baltic Sea, and the Gulf of Mexico.
Read more about Anoxic Waters: Causes and Effects, Anoxic Basins
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“You could not step twice into the same rivers; for other waters are ever flowing on to you.”
—Heraclitus (c. 535–475 B.C.)