SUMMARY
The limnological conditions of the Arroz Lake, Careiro Island, central Amazon, are determined by the River Solimões, since they are linked almost all year round. The water level varies annualy between 7 and 9 meters with peak levels in June and lowest levels in January. This cycle is the principle factor determining the great physical chemical and biological variations which occur in the lake.
The chemical analysis clearly demonstrate the seasonal variations in the Arroz Lake: stagnation, with a clear separation between the epilímnio and the hipolímnio, temperature stratification, total salt content and the presence of complex notable agents during the high water and the total moisture during lowest level water.
From September onwards the lake receives an intense migration of fish of the Loricariidae family, more commonly known as "acari-bodó" (65.000 of these fish were captured by six fishermen between September to December). These fish provoke as intense resuspension of green sediments in the lake, since in laying their eggs they dig holes up to twenty centimeters deep in the mud. That recirculation jointly with the effect of the wind causes the resuspension of the sediments, increasing the quantity of dissolved mineral salts. This phenomenon causes several anomalies which permit an elevated degree of recycling of nutrients, and primary production, which practically determines the absence of stratification of the sediments.