It is paramount that the richest diversity of freshwater fish species on the earth is protected not only for its intrinsic value but also for its far-reaching extrinsic value to humans and entire ecosystems. This study therefore focuses on the effects of naturally occurring phenomena, such as drought, and anoxic events, on the icthyofauna of five ox-bow lakes at one Amazonian area of the Yavarي River, Perْ. The data have been used to assess the effectiveness and reliability of fishing methods and to monitor changes in diversity, abundance and richness across the three years of 2005, 2006 and 2007 in line with normal, drought and anoxic events respectively.This study concludes that fish in Amazonian lakes are well evolved and adapted to cope with naturally occurring fluctuations in water levels and specifically with droughts during the dry season. From this study, it also becomes apparent that local and trans-boundary monitoring, management and regulatory schemes are needed.