The habitat conditions of algae Desmidales in the sphagnum bogs of the Khanty-Mansiysk Autonomous Okrug ‒ Yugra are analyzed. The results of studies of desmid algae found in the swamps of the region are presented, their spatial distribution is indicated. The dominant species of Desmidiales include: Actinotaenium cucurbitinum, Actinotaenium rufescens, Bambusina borreri, Closterium baillyanum, Pleurotaenium minutum f. minus and Staurastrum dilatatum. The uneven development of algae in the research areas was established. The limiting effect on the species composition and number of cells is the pollution of water and swamp mass with oil and oil products, low water temperature, and insufficient illumination. The highest qualitative and quantitative indicators of desmid algae were obtained at pH 3.5, water temperature in the range of 13.0–25°C, under open water conditions.

An ecological and floristic phytoplankton assessment of the Ob River in one of its middle course segments, located at high latitudes, was carried out. A rich algological community was observed, based on the summer and autumn field material, with the composition noticeably changed since earlier studies carried outin 1996. The top 10 families comprise more than a half, and the largest 8 genera include 33% of all observed algae.Under conditions of pH close to neutral, the main factor influencing the formation of species diversity, total abundance and structure of the identified phytoplankton is water temperature. Thestudy also features the floristic comparison of the Ob River plankton algocenoseswith those of other large rivers: Lena, Irtysh, Dnieper, Volga. The prevalence of planktonic, widespread, oligohalobial, betamesosaprobic varieties and forms of algae, which prefer a neutral medium reaction, was revealed in the studied phytoplankton.