— Data are presented on fish community structure in ponds and floodplain and mainland lakes in the southern taiga subzone of Western Siberia (within Tomsk region), where a total of 14 fish species have been recorded. The ordering of data on the fish biomass using a factor classification program has allowed us to distinguish three population groups, with one of them including three subgroups. Winter hypoxia is the most important among external factors determining the structure of fish communities. Its absence determines the presence of perch in the fish communities; in turn, the abundance of perch affects the abundance of other fish species. Therefore, the primary organization of the communities is determined by the environment and their secondary organization by the relationships between the species.