The Aral Sea, a terminal lake fed by two major rivers, the Syrdarya and Amudarya forms a natural border between Kazakhstan and Uzbekistan. In 1960 it was the fourth largest lake in the world; today it is on the verge of deteriorating into a small and dirty waterhole. The destruction of the Aral Sea is an example of how quickly environmental and humanitarian tragedy can threaten a whole region. The destruction of the Aral Sea is a textbook example of unsustainable development.