Ounianga Serir, the third and largest lake in Northern Chad, is in the process of being cut into pieces by fingers of sand that blow through breaks in the surrounding cliffs. The heat and strong wind cause a high rate of evaporation that has turned the potable groundwater into a lake that is saltier than seawater and devoid of fish. The lakes here have slightly different elevations, and the higher ones are less salty. The lake is punctuated by ship-like islands of Nubian sandstone, the permeable rock that stores and transports the water underground, and it is stained white by salts leaching out by evaporation. Maps from aerial surveys in 1954 show the lakes being larger and more connected, indicating that the water level has dropped.
