Jamileh Panahy Mirzahasanlou - Assistant Prof., Department of Biology, Faculty of Basic Science, Gonbad Kavous University, Gonbad Kavous, Golestan, Iran
Taher Nejadsattari - Associate Prof., Department of Biology, College of Science, Tehran Science and Research Branch, Islamic Azad University, Tehran
Zohreh Ramezanpour - Assistant Prof., International Sturgeon Research Institute, Rasht, Iran
Javid Imanpour Namin - Associate Prof., Department of Fishery, Faculty of Natural Resources, University of Guilan, Some Sara, Guilan, Iran

Diatoms are one of the most commonly used organisms in water quality assessment studies and several diatom based indices have been developed to assess water pollution and trophic status of aquatic ecosystems. Biological Diatom Index (BDI) provides valuable data about the trophic status of the aquatic environment. In this study epilithic diatoms were collected from 6 stations from October 2013 through September 2014 along the Balikhli River. Total of 77 species were identified form which 47 species were used to calculate BDI to assess the trophic status and water quality of Balikhli River. According to results obtained in this study the sampling station 2 showed low water quality and classified in Meso- Eutrophic state, while all other stations maintained Moderate water quality with Mesotrophic state

Algae, Water quality, Biological Diatom Index, Balikhli River