Aquatic ecosystems are sustainable and dynamic, that they are important for their biological and geographical diversity. Reservoirs are complex ecological and dynamic systems which have a close relation to human activities. They are not only the major potable water resources but also they provide various habitats with medium hydrological cycles for plants. Eutrophication by following into them process usually results in destruction and instability of plants and animals populations. So, for conservational porposes and sustainability, Trophy status of the lake should be studied. The aim of this study was to evaluate the trophy of Zayande Roud River Reservoir (ZRRR) during spring and summer seasons. Sampling was performed from April to September 2011, in four stages at 45 days intervals to achive this goal physicochemical (temperature, dissolved oxygen, pH, EC, Secchi disc depth and nutrient levels) and Chlorophyll a level were measured. Trophy state was determined according to OECD kashida; TEXT-ALIGN: justify; LINE-HEIGHT: 90%; TEXT-KASHIDA: 0%; MARGIN: 0cm 0cm 10pt" Key words: Eutrophication, Mesotroph, OECD, Oligotroph, Trophy state, TSI, Zayande River Roud reservoir
