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The River Niger is the third longest river in Africa, with a stream length of 4200 km, a drainage basin of 2 170 500 km (of which 1 500 000km(2) is an active basin), and an average discharge of about 6000 m(3)/s. The natural variability of its rainfall and discharge are analysed for several major sub-basins, in the context of the West African drought, which has lasted for nearly 40 years. Two paradoxes are shown: the increase of Sahelian runoff since the beginning of the drought due to land degradation, and the steep decrease of Sudanian runoff over the same period, substantiated by the long-lasting decrease of the groundwater tables. The cooperation between the nine countries sharing the basin is organized through the Niger Basin Authority (NBA), which needs to propose and administer plans to meet objectives for all development projects throughout the basin. Much information about the water resources available in the basin is collected and analysed by the NBA, which is summarized in this paper, including surface and groundwater resources, rainfall and evaporation over the basin, existing and projected dams and water consumption for irrigation. From the standpoint of water resources, the Niger basin can be divided into four zones with different physical and geographical characteristics: (i) the Upper Niger basin, in Mali, Guinea, and Ivory Coast, covering a surface of 257 000 km(2), with only one large dam in Mali (Selingue, 1.7 MMm(3)); (ii) the inner delta, in Mali, which seasonally flooded surface can reach 35 000 km(2), and where the water losses vary between 24% and 48%; (iii) the Middle Niger basin, in Mali, Niger and Benin, where local flows from Sahelian and Sudanian areas join the residual outflow from the inner delta; and (iv) the Lower Niger basin, between Cameroon, Nigeria and Chad, where high rainfall increases the River discharge, and where large dams for hydro-electric power production and irrigation are built. The River Niger is deficient in dams to control water, especially in its upper and middle basins. Nigeria has many dams, including large dams, while Burkina-Faso has many small dams, but there are only a few dams upstream of the River Niger in Mali/Guinea/Ivory Coast. It is therefore likely that several dams will be built in the Niger basin in the coming years, and several are in the project phase: among which three are large ones in Guinea (Fomi), Mali (Tossaye) and Niger (Kandadji). All of these will have a large impact on the River Niger regime and the environment, especially the Fomi dam, which will significantly change the river regime upstream of the inner delta, inducing an important reduction of the flooded area, and the Tossaye dam on the Saharan border of Mali, which could promote a very significant level of evaporation, while the Kandadji dam will have less impact downstream. It is very important before building these dams to take into account the past years variability of climate and river regime. It is particularly important to take into account the very large runoff decrease in the tropical humid sub-basins, and the runoff increase in the Sahelian sub-basins.