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Geography

The Niger River is a relatively clear river, carrying only a tenth as much sediment as the Nile because the Niger's headwaters lie in ancient rocks that provide little silt. Like the Nile, the Niger floods yearly; this begins in September, peaks in November, and finishes by May. An unusual feature of the river is the Inner Niger Delta, which forms where its gradient suddenly decreases. The result is a region of braided streams, marshes, and large lakes; the seasonal floods make the Delta extremely productive for both fishing and agriculture.

The river loses nearly two-thirds of its potential flow in the Inner Delta between Ségou and Timbuktu to seepage and evaporation. The water from the Bani River, which flows into the Delta at Mopti, does not compensate for the losses. The average loss is estimated at 31 km /year but varies considerably between years. The river is then joined by various tributaries but also loses more water to evaporation. The quantity of water entering Nigeria was estimated at 25 km /year before the 1980s and at 13.5 km /year during the 1980s.

The most important tributary is the Benue River which merges with the Niger at Lokoja in Nigeria. The total volume of tributaries in Nigeria is six times higher than the inflow into Nigeria, with a flow near the mouth of the river standing at 177.0 km /year before the 1980s and 147.3 km /year during the 1980s.