Tropical rainforest regions have large hydropower generation potential that figures prominently in many nations’ energy growth strategies. This paper argues that feasibility studies of hydropower plants typically ignore the effect of future deforestation or assume that deforestation will have a positive effect on river discharge and energy generation resulting from declines in evapotranspiration (ET) associated with forest conversion. Forest loss can also reduce river discharge, however, by inhibiting rainfall. This study used land use, hydrological and climate models to examine the local ‘direct’ effects (through changes in ET within the watershed) and the potential regional ‘indirect’ effects (through changes in rainfall) of deforestation on river discharge and energy generation potential for the Belo Monte energy complex, one of the world’s largest hydropower plants that is currently under construction on the Xingu River in the eastern Amazon.