Abstract: The qualitative and quantitative characteristics of zoobenthos and zooperiphyton of two model oxbow lakes in the Middle Ob basin are presented. Three sites in each oxbow lake are examined: the apex (or “pond”) site least connected with the river, the middle part, and the site near the channel flowing into the river. The specific longitudinal structure of the taxonomic composition and the abundance of zoobenthos and zooperiphyton has been revealed. The most favorable conditions for zoobenthos are in the pond site and, for zooperiphyton, they are in the middle of an oxbow lake and near the channel. In order to identify and understand the general patterns of aquatic ecosystem functioning, the results are discussed in light of well-known theoretical concepts: the ecotone, the edge effect, and the lake continuum.