The Lakes of Ounianga in the Sahara Desert, Chad

Lakes of Ounianga are a series of 18 lakes in the Sahara Desert, in northeastern Chad. They are found in a basin between the mountains of Ennedi East and West Tibesti. Names of nearby villages are used to name the lakes. The lakes were created as an addition to the original. The lakes were declared a UNESCO World Heritage Site in 2012.

Lake in the Ounianga Serir, northern Chad (© George Steinmetz Corbis).

Ounianga lakes

Lakes of Ounianga, Chad, are located in a hyper-arid desert with a minimum of 2 millimetres of rainfall per year. The ancient water flows from a shallow basin beneath hills and sandstone cliffs. This unique hydrological system can sustain the largest permanent freshwater lake in an arid desert environment in the world. Ounianga lakes are remnants of a single, large lake that once occupied the basin about 5,000 to 15,000 years ago. The climate changed over the millennia, and the lake began to shrink. Large, wind-driven dune invasions of the depression caused it to be divided into smaller basins.

These 18 Lakes are divided into two groups, the Ounianga Sérir group and Ounianga Kébir, each about 40 km apart in the Ounianga basin. They differ in their chemical composition. Some are so salty that they cannot support basic life forms, while others can sustain aquatic plants and fish. The Ounianga Sérir is about 45 to 60 kilometres southeast of Ounianga Kébir, and Lake Teli is the largest lake and one of the most important for biological reasons. It has a total surface area of 4.4 km² with a maximum depth of 10 metres. The water level in the lakes varies between 350 and 380 metres above sea level. Its freshwater supports a wide range of life. Lakes under the Sahara Desert: because the sandy substrate is porous, water can flow freely underground. Lake Teli and 13 smaller lakes are part of the eastern group.

The second group of four lakes in the Ounianga Kébir is located further west. It is dominated by Lake Yoa; it is 3.6 km² and 27m deep. This hypersaline lake supports algae and a few microorganisms. The rocks surrounding the lake are covered in white salt deposits. A sprawling village with approximately 9,000 inhabitants lies among the hills and dunes nearby. Lake Motro is located about 30 kilometres southeast of Unianga Kébir. This is the village that is habitable on the trans-Saharan truck route to Libya.

The ancient freshwater lakes of Ounianga, Chad, in the Sahara Desert

Lakes in the Ounianga Sérir have freshwater, such as Obrom, Idem, Aujou, Boul, Hogo, Djiara, Aolta, Daleyda, and Boulkou, and another in their immediate vicinity, Lake Eliné, has saltwater.

These Sahara Desert lakes' Dark surfaces are almost entirely segregated by orange-coloured sand dunes, which flow from the northeast into the depression. One of the nearby lakes has an evaporation rate exceeding 6 metres per year, due to the northeast winds that blow almost all year and the cloudless skies. The Ten Lakes are saline, despite the arid climate.

The freshwater lake in the Sahara Desert causes the apparent paradox. The Ounianga Depression is where freshwater from a large aquifer flows into the desert's heart. Despite the high evaporation rate, the aquifer is large enough that it can continue to supply water to small lakes. Floating reeds also reduce evaporation. These lakes create a unique hydrological system in the Sahara Desert.

V-shaped lakes — The northeast desert wind blew, carrying sand from the plateau up through the land. It deposited it right where farmers were planting crops. The lake dwellers realised that the sand would eventually choke their crops and orchards, so they built barriers to prevent such an outcome. Aerial photos clearly show these barriers at various locations between Ounianga Kebir and Serir. These barriers appear in the form of a series of "V"s like VVVVV. It would have taken many people to build the layers of barriers visible today, which appears extraordinary.

First image credit: eMRaistlin Uth Majere