The Parana River hydrosystem harbors a large and diverse community of freshwater biota. The Middle Parana River and its main tributary, the Paraguay River, are also an important inland artery for commerce and, up to day, their floodplain had suffered a moderate human impact, yet. The river-floodplain system maintains its aquatic habitat heterogeneity and the natural connectivity between lotic and lentic water bodies. The present review focuses on the description of the main lotic and lentic habitats of the Middle Parana ecosystem as well as their hydrosedimentological relationships throughout the pulsing river regime. Aquatic habitats are classified according to their location at the main channel and within the floodplain. The hierarchical/functional classification of the floodplain channels is based on the mean annual discharge and it, degree of intermittence. The relationships between river dynamics and the floodplain lakes evolution as well as the influence of the autogenic processes on the waterbodies are also described. The conservation of the ecological integrity and the management of aquatic ecosystem of the river requires a thorough understanding of its ecological habitats. the biotic communities, and their interrelationships. This paper examines the present state of our knowledge of the hydromorphological changes in the Middle Parana aquatic habitats and describes the communities of fishes and benthic macro invertebrates associated with them.
