The paper presents the results of a study of phytoplankton in Lake Munozero during the vegetation period in 2018. The seasonal dynamics of the biomass and abundance of algae in the southern and northwestern reaches experiencing different anthropogenic pressures has been considered. The reservoir stands out among other water bodies of the Republic of Karelia for its chemical and morphometric characteristics. It is characterized by high mineralization (up to 100 mg/l), isolation of the reaches, low color and content of nutrients and organic compounds. There have been identified 147 taxa of the algoflora with a rank lower than the genus, belonging to 9 divisions. The structure of algocenoses in terms of species richness and quantitative development is determined by representatives of centric diatoms, cyanobacter, dinophytes, and chlorococcal greens, which is important for the formation of the fish food base. Average size of phytoplankton during 2018 in the northwestern reach reached 492 thousand cells/l, the average biomass was 0.468 g/m3. The average size of phytoplankton in the southern reach reached 589 thousand kg/l, the average biomass was 0.459 g/m3. The water quality in the northwestern and southern reaches by the value of the saprobic index corresponds to the III class of waters, but the biomass values characterize both parts of the reservoir as oligotrophic. Shannon's index, quantitative and structural characteristics of phytoplankton differ in the northwestern and southern reaches, seasonal dynamics is not typical for phytoplankton of the oligotrophic Karelian lake. According to the data on abundance and biomass of phytoplankton of Lake Munozero the value of commercial fish catch was calculated.

The paper presents the results of a study of the phytoplankton of small Lake Vendyurskoe (south of Karelia) in the spring ice period, in summer and autumn seasons of 2020. The dynamics of quantitative and structural indices of lake algae during the trout farm operation is considered in comparison with the indices of previous years. For the studied seasons of 2020 there were identified 122 taxa of algal flora belonging to 8 divisions. The structure of algocenoses can be characterized by rich species diversity and quantitative development as diatom green structure with golden algae insertions. In autumn the representatives of cyanobacteria were encountered en masse in some areas. Phytoplankton abundance in the spring ice period varied within 612 thousand cells/l - 2188 thousand cells/l, the biomass reached 2.9 mg/l with a minimum value of 0.1 mg/l. Phytoplankton abundance for the studied summer period of 2020 averaged 2216±796 thousand cells/l with a maximum value of 3986 thousand cells/l, the average biomass in the lake did not ex-ceed 1.325±0.504 mg/l. Phytoplankton abundance in autumn averaged 4934±1665 thousand cells/l with a maximum value of 7832 thousand cells/l; biomass averaged 5.8±1.5 mg/l with a maximum value of 7.9 mg/l. According to the eco-logical and geographical characteristics, most representatives of the algal flora found in the lake are widespread freshwater organisms belonging to the planktonic flora and preferring a neutral reaction of the environment. The Shannon index increased from 2.8 in the center of the lake to 3.3 in the trout farming area, which indicates good species diversity. The Sorensen index of 0.8 revealed the homogeneity between phytoplankton communities in different areas of the lake. Most of the identified types of saprobity indices belong to the representatives of the β-mesosaprobic and oligo-beta-mesosaprobic zones (up to 78% of the total number of identified indicator species). The saprobity index corresponded to the 2nd class of water purity (pure, α-oligosaprobic), which is due to the species composition of the dominant phytoplankton complex, however, the biomass indicates that the lake belongs to the 3rd class of water purity (satisfactorily clean, β-mesosaprobic).