In different types of water reservoirs of the river Aragvi basin 263 taxa of 3 classes, 12 orders, 26 families and 45 genera. The order Bacillariophyceae is represented by the highest number of species, the number of which is 216, i.e. 82% of the total number of the diatom species recorded on the study area. The class Fragilarophyceae is represented by 45 taxa, i.e. 17% of the total number of the recorded diatoms. The class Coscinodiscophyceae is represented by only 2 species (1%). Of the species of Bacillariophyceae the following orders are lading by the number of species present: Naviculales (80), Cymbellales (47), Bacillariales (43) and Achnanthales (20). In the class Fragilariophyceae the order Fragilariales is the most diverse on the studied area. The majority of the diatoms recorded by us in the rivers of Aragvi basin are benthic, while phytoplankton is better developed in lakes. In all types of the water bodies species of the following genera are the most frequent: Diatoma, Cymbella, Navicula, Synedra, Gomphonema, Nitzschia,Hannaea, Cocconeis, Fragilaria.