Lake Débo is a lake in the central part of Mali, formed by the seasonal flooding of the Niger River basin. It is in the Inner Niger Delta of the Niger River. During high water stages of the river, the delta formed by lakes, creeks, and backwaters form part of Lake Débo. The inner delta has many wide channels, which are shallow and flooded marshes; this delta extends over a length of with a width of . Lake Débo during high flow season, is at a distance of from Mopti on its upstream, on the southern end and from Timbuktu at its downstream, on the north-eastern end. It is the largest of many such seasonal wetlands and lakes which form the Inner Niger Delta, and the largest lake within Mali. Its size is largely reduced during the dry season of September to March. The existence of this lake called the "Great Lake" in the inner delta of Niger River between Jenne and Timbuktu in Mali has been established after extensive study of maps of the region extending over a period from 1000 to 1900 AD; 400 maps were studied for the period.
History
This lake, called the "Great Lake" in the inner delta of Niger River between Jenne and Timbuktu in Mali, was known to Europeans from very early times. The earliest known report of it was in the first millennium BC. Ptolemy described it as having the shape of a barbell. Study of more than 400 maps of the region created over a period from 1000 to 1900 AD found that the lake appeared on 95 percent; the only feature depicted on more maps was the Nile. The lake has been known variously as Nigrite Palus, Lake Sigisma, Lake Guber, Lake Guarda, Bog/Morais of Guarda, Lake Maberia, Bahar Seafeena, Lake Dibbie, but it is now known as Lake Débo. The Niger River is assessed as a young river of 2000 years age and is yet to stabilize. However, the natural channels have undergone many meandering changes.
Geography
The lake is formed upstream of the confluence of Niger and Bani Rivers. It is the best known lacustrine lake in Mali, which has diameter of and shallow and hence large vessels can not pass through the lake. In the upper highland reaches of these rivers, the highland terrain slopes are very gentle resulting in the retardation of flows and creation of this lake. The slope reported before the creation of the lake is per . The lake is divided by a barrier into two zones, the upper and the lower. The barrier extends several kilometres southwards. Beyond the barrier, the lake is narrow and long and its outreach is not visible. The Bara Lisa River joins the Niger above Dire. It exits the deltas from the northern shores of Lake Debo and flows east. The Issa Baris, the main arm of the lake, exits from the lake in a westerly direction and turns northeast to join the Bara Lisa.
Geological formations recorded at the bed of the lake are "from dense crystalline rock of Precambrian sandstone compacted in the broad Taoudeni Syncline as an alluvial fan and covered by a hard layer of cemented-laterite." The flat slopes and geology of the beds has resulted in creating a meandering and multi-channel flow pattern, which has resulted in the formation of inner delta of the Niger. The inner delta thus has many wide channels, which are shallow and flooded marshes; this delta extends over a length of with a width of . It is inferred from the study of nearly 400 maps that it is the delta which is the origin of the lake and that the lake is the largest in the delta. It is integral to the wide river channel with its size fluctuating with variation of the water level in the lake. It also provides confirmation of the nature of blocked water and also includes the Erg of Bara region. The maximum flood in the lake and the delta occurs during November and December.
Below Lake Debo, the Niger valley is marked by a large number of lakes, which are lower than the river level. As part of the central delta, the lake is the largest. As it is a part of the Niger River, its size varies with the fluctuation in the water level. and maximum flood occurs in the river during November and December. The lake has a vast expanse of water extending on all sides. The river that is formed at the outlet of the lake has a width of for a length of downstream, where after it narrows down, gets spilled into many channels; marshy islands are formed and depth of water is in the range of . Foolahs, the nomads who live here, use these marshes as pastures in the dry season and thereafter they go back to their habitats in the interior of the basin.
