Usually a wetland is presented as a heterogeneous complex, such that any analysis of its aquatic bird diversity should compare different levels (alpha and beta) with the gamma diversity of the landscape. Habitat heterogeneity may affect the structure and composition of these species assemblages, yet this subject has been little studied in Chile. The objective of this work was therefore to characterize aquatic bird assemblages in a southern Chile wetland. A series of counts was made for each wetland type present in the complex to characterize bird assemblage structure using alpha and beta diversity, abundance of species and density. The alpha diversity was significantly different among the four types of wetlands studied. Seasonal and spatial variations in the diversity, abundance and density of wetland types were analysed and compared with the expected gamma diversity. The beta diversity of the Lanalhue complex represents > 20% of the gamma diversity.