Human modification of a large meandering Amazonian river: genesis, ecological and economic consequences of the Masisea cutoff on the central Ucayali, Peru.

Evidence is mounting regarding the significant extent and scope of long-term human modification of "pristine nature" in the neotropics. In Amazonia, recent studies point to the landscape imprint of human activity that has transformed the forests, savannas, soils, and waterways of the basin. In this report, we describe a massive meander cutoff in the Peruvian Amazon along the Ucayali River--the fifth-longest river in the Amazon basin--that was triggered by small-scale human actions and resulted in significant ecological and economic consequences for the region. The modern case of the Masisea cutoff-near the Amazonian port city of Pucallpa, Peru (285,000 inhabitants)-indicates that humans using simple tools can play a major role in transforming large meandering rivers and their floodplains.