Lakes and reservoirs are considered by human communities as an important supply of potable and agricultural water, therefore some sort of water quality monitoring required in order to use the water resources effectively. Pollution is one of the reason for algae bloom and eutrophication in the aquatic ecosystem which finally leads to the lower water quality and biological diversity. Zayandeh Roud dam lake is located in central region of Iran and is the main source of fresh water for its numerous inhabitants in the region. The aim of the present study is to investigate the state of trophy and trend of changes in Zayandeh Roud dam lake in 2013. Sampling was carried out at 45 days intervals from April 2013 to March 2014 at five sampling stations. To determine the state of trophy in the lake physicochemical parameters such as temperature, dissolved oxygen, Secchi disk depth of appearance, pH, total phosphorus, total Nitrogen ,COD, BOD, EC, TDS, TSS and levels chlorophyll a were measured at each sampling period. To determined the trophic state in the lake. OECD mesotrophic and oligotrophic , respectively. Key words: Zayandeh Roud dam, Eutrophication, TSI indicator, Mesotrophic, Oligotrophic Trophic state
