One of the consequences of industrial, agricultural and urban development is the increase of water pollution. Water supply for various consumption has considerable importance in the arid and semi-arid regions. Development of industries and agricultural activities around the Zayandehrud river, where is located in the central plateau of Iran, has been caused environmental and ecological problems within Zayandehrud basin. Zayandehrud river has been receiving industrial wastewater, drained water from agricultural activities as well as urban and village wastewater. Surface water quality assessment through permanent monitoring is the base of a program for controlling and decreasing of river pollution. Due to their simplicity of application, water quality indices (WQI) can be playing great importance role as one of the methods for determining the water pollution. In order to calculate water quality indices (NSFWQI, BMWP and ASPT) as well as richness and biodiversity indices of benthic macroinvertebrates, eight stations were selected in Zayandehrud river from Baghbahaderan to Zyar. Water and substrate samples were collected monthly from July 2006 to June 2007. The results of Zayandehrud river zoning on the base of NSFWQI m showed that the quality of Zayandehrud water is not acceptable. During the period of study, %63.5 and %36.5 of calculated data for this index were corresponded to the "moderate" and "poor" quality Shannon diversity index, the river was categorized as "moderate" and "substantial" pollution Keywords: Zayandehrud river, WQI, Benthic macroinvertebrates, Biodiversity, Biotic indices
