Daniela Granato-Souza will be presenting her research that draws together historical sources and tree-ring reconstructions of wet season precipitation extremes in the eastern Amazon during the late 18th- and 19th-centuries. The historical accounts describe ship groundings on the Amazon River, crop failure, livestock mortality, and water shortages during many of the tree-ring reconstructed drought extremes. Heavy rains and flooding on major rivers are described during the wet extremes. The “Unknown Drought” of 1865 was the lowest single wet season precipitation total reconstructed with tree-rings in the eastern Amazon from 1759-2016 and appears to have been one of the lowest stream levels observed on the Amazon River during the historical era. The economic impact of the drought in 1865 was mitigated in Brazil by the highly inflated price of cotton due to the collapse of production in the American South during the Civil War, and is one reason why the magnitude of the moisture deficit and low water conditions on the Amazon during the Unknown Drought of 1865 have received limited historical or scientific attention.