“Proxy tree-ring and historical evidence for precipitation extremes during the preinstrumental nineteenth century indicate that recent floods and droughts on the Amazon River may have not yet exceeded the range of natural hydroclimatic variability.
The most severe and sustained drought in the history of instrumental precipitation and streamflow observations for the Amazon River basin occurred in 1925/26 when river commerce was brought to a standstill and several steamships became grounded in the low water conditions between Iquitos and Manaus, Brazil, and on the lower Amazon River in the state of Pará”
