The Amazon drainage basin extends over more than 6×106 km2 and discharges a mean annual flow of 209 000 m3 s-1 into the Atlantic Ocean. The specific discharge distribution over the whole drainage basin shows a strong regional tendency, with low values for the southern tributaries (Xingu, Tapajos, Madeira, Purus, Jurua), which present an austral tropical regime, but higher values for the northern tributaries of the equatorial area (Ica, Japura, Uaupes-Negro) which present an equatorial transition regime or a boreal tropical regime, like the Rio Negro river for example. This regional variability is obviously correlated to the rainfall. The Solimoes-Amazonas river is characterized by an equatorial regime altered by the yields of the different tributaries, with a hydrological maximum in May upstream and in June downstream and a seasonal variability which is very low. During the 20 year study period (≈1970-1990), the inter-annual variability of the mean discharge was very low along both the Solimoes-Amazonas river and its equatorial tributaries. This variability is higher in the drainage basins where the specific discharge and, of course, the rainfall are lower, for instance in the case of the Rio Branco river and of the southern tributaries.