Diatom analysis is one of the methods of paleolimnological research, with the help of which it is possible to determine the state and development of aquatic ecosystems in the past and present. Assessment of the current state of reservoirs is of great importance in paleolimnology, it will allow to obtain results about temperature regime, mineralization, pH environment and water quality. The research area is a region with a lot of small polygonal reservoirs that react quickly enough to external environmental changes that are formed during the cracking of re-vein ice and may form large reservoirs in the future. In this work, the IP-1 monitoring reservoir of the Kytalyk locality was studied for 10 days (every three days) during the expedition work carried out in 2011 using standard methods and a set of field equipment. The material of the study was phytoplankton samples, as a result of which the taxonomic composition of the diatom flora was investigated and the water quality of the Kytalyk monitoring site located in the basin of the Berelyakh river, the left tributary of the Indigirka, was determined.