The larger of the two lake groups, Ounianga Kébir sits adjacent to the main settlement and contains the most visually dramatic water of the entire system. The group includes around a dozen lakes in close proximity, with water chemistry ranging from mildly brackish to intensely hypersaline.
Lake Yoa is the most studied and most famous of the group — a deep, stratified lake whose sediment layers preserve a continuous 10,000-year climate record of the Sahara. Swiss scientists have cored the lakebed and extracted a chronology of wet and dry periods reaching back to the African Humid Period. The surface water is highly saline; below a density boundary, anoxic water sits undisturbed and has accumulated organic sediment without disturbance for millennia.
Lake Katam is smaller and more accessible from the shore, with striking reddish water caused by blooms of the salt-tolerant alga Spirulina. The contrast between the orange-tinged water and the surrounding dunes is one of the most photographed images from this part of Chad.
Ounianga Kébir town itself has a small market, a fuel supply that is sometimes available, and a military post where permits must be registered. There is no hotel — travelers camp.