Well being and development of community rely on renewable fresh water for drinking, irrigation of crops, and industrial uses. Hence, monitoring of the water quality and its trophic state nowadays, becoming increasingly important issue. In many regions of the world, human activities including agricultural expansion and increasing usage of fertilizer, sewage discharges, urban runoff, leaking septic tanks, and erosion of stream banks can increase the flow of nutrients and organic substances into reservoirs and lakes. These substances often overstimulate the growth of algae and aquatic plants in water body, resulting in eutrophication and hence, affecting diversity, species richness, and ecosystem performance. At present study the trophic state of Zayandeh Roud Dam Reservoir was determined by measuring physico-chemical and biological parameters including; pH, dissolved oxygen (DO), electrical conductivity (EC), temperature, biological oxygen demand (BOD), chemical oxyge demand ( COD ), total nitrogen (TN), total phosphate , secchi disk depth of appearance, TDS , TSS and chlorophyll a. Determination of trophy status of the dam reservoir were also carried out by using OCED justify; MARGIN: 0cm 0cm 10pt; mso-line-height-alt: .8pt" Keywords: Zayandeh Roud Reservoir, Eutrophication, Trophic State Index (TSI),Trophic state
