The scientific lecture with the title of "IRWQISC Index and TSI in Chitgar Lake 2013 - 2020" was presented by Mr. Ali Abedini in the conference hall of the research institute. In this lecture, hydrochemical data and water quality index as well as trophic state index in the Chitgar Lake located in the west of Tehran (District 22) were reviewed. According to the data, the ratio of nitrogen to phosphorus in this lake has been more than 30. Therefore, in the years under review, phosphorus has played a limiting role in the process of eutrophication. Based on multi - parameter evaluation, at the beginning of the flooding of the Chitgar artificial lake from 2013 to 2020, the trophic state index was less than 40 and in other words, it was about the level of ultra - oligotrophic lake. However, in 2015 - 2016, it approached the mesotrophic level and again in 2018 - 2019, it had a downward trend. Although the trophic state index (TSI) in Chitgar Lake has not exceeded the level of oligotrophic lakes and the Water Quality Index (WQI) has not fallen below the middle class by 2020, but considering the function and objectives of the construction of this lake, it is necessary to pay maximum attention to prevent excessive richness of nutrients in the lake and to take measures to maintain water quality and prevent eutrophication. Therefore, in addition to keeping the water purification system active through the wastewater treatment plant, it is necessary to biologically control the balance of living organisms in Chitgar Lake.