The river's total length is and its drainage basin totals in area, providing a mean discharge of around of water per year. The river is navigable for over . All of the water comes from the high mountains in the south where annual precipitation can be over . Even before large-scale irrigation began, high summer evaporation meant that not all of this discharge reached the Aral Sea – though there is some evidence the large Pamir glaciers provided enough meltwater for the Aral to overflow during the 13th and 14th centuries.