The flood pulse is a key factor in the ecological processes of the varzea. This study aims to describe water level variation at a varzea site in the Middle Solimoes river region (Amazon River). The study took place in Mamiraua Sustainable Development Reserve from 1990 to 2008. During this period, water level varied between a minimum of 21,71 and a maximum of 38,55 meters above sea level. Average annual amplitude was 10,60 meters (n =17, s.d. = 1,84). The three highest water levels were registered in 1997, 1998, and 1999, whereas the lowest were registered in 1991, 1992, and 1995. The study showed that high water level periods, or floods, occur from May until mid-July, whereas low water levels, or dry periods, occur in the months of September, October, and November. Flooding periods begin in the end of November and end in the beginning of May, whereas, drying periods - when water levels fall - start mid-July and end in the beginning of September. The annual flooding pattern has followed a similar model created from monthly water level averages. Markedly different oscillations were observed in 1992, 1995, 1997, and 2004. Through the monitoring of water level variations in the Mamiraua Reserve it was possible to characterize the flood pulse in the middle Solimoes river region - a variable to be compared with other environments in the Amazon basin.