Guelta

A guelta is a special form of a natural waterhole in the Sahara. It may be a natural cistern filled with water in a rock formation or a relatively fast evaporating larger puddle in an otherwise dry wadi, which has formed after a rain event. The permanently filled Gueltas, like the one shown, or guelta d' Archei in Chad, are usually caused by groundwater, which is pressed from the surrounding lowlands to the surface, forming thereby constantly filled with ponds and reservoirs. Amazingly, these waters are the number and types of creatures living in it. In guelta d' Archei in Ennedi massif, there is still seven crocodiles.