A biological assessment of the Tang Sorkh River (Iran) was studied from July 2013 to August 2014 using benthic macroinvertebrate communities. Samples were gathered every two months, from five stations using a Surber sampler( 30×30cm), fixed in formalin (4%) and then separated and identified in the laboratory. Environmental conditions (current velocity, temperature, depth, width, dissolve oxygen, conductivity, pH, alkalinity, Total Suspended Solids (TSS) and grain size) were measured. In addition, diversity and biotic indices were used to determine the water quality of the river. Results showed that 5 classes, 9 orders and 20 families were identified in this river. The families Hydropsychidae (Trichoptera), Simuliidae (Diptera) and Baetidae (Ephemeroptera) were dominant. Shannon-wiener and Simpson indices showed the highest diversity at station 1 and the lowest diversity in station 4. According to the Hilsenhoff, ASPT and BMWP indices, station 1 had good water quality for aquaculture.

Keywords: Macrobenthic communities, Diversity index, Biotic index, Tang Sorkh River