The data on taxonomic composition of phytoplankton in floodplain reservoirs of various types (chute, oxbow and oxbow lake) of the Upper Ob served as an subject of the present study. The total taxonomic diversity amounted to 78 taxa (genus definition) belonging to 7 divisions: Bacillariophyta - 24 genera, Chlorophyta - 27, Ochrophyta - 11, Cyanobacteria - 8, Dinophyta - 4, Euglenophyta - 3 and Cryptophyta - 1 genus. Diatoms dominate in the number of taxa in the chute presented by the Bacillariophyta division; in oxbow and oxbow lake representatives of the greens, division Chlorophyta. There is the highest frequency of occurrence of large taxa: in the chute - diatoms 83.3 % and green - about 58.3 %; in the oxbow - single-celled golden - 91.9 %, green - 82.0 % and diatoms - 72.7 %; in the oxbow lake - golden -82.0 % and diatoms - 54.5 %. The maximum phytoplankton biomass values were detected in the lake in spring at the end of April - 4551.6 mg/m3, while in the chute the maximum for this indicator was reached only in mid-June - 673.1 mg m3. For the oxbow, the top of phytoplankton biomass was noted in early June - 1947.8 mg/m3 and in the end of July - 1807.0 mg m3. According to the biomass level of phytoplankton, lake and oxbow belong to mesotrophic reservoirs (up to 1.0 - 5.0 g/m3), the chute - oligotrophic (up to 1.0 g/m3).