en Ecology Ecology پژوهشي Orginal research papers <font face="Times New Roman" size="3"> </font><p class="MsoNormal" style="margin: 0cm 0cm 0pt text-align: justify line-height: 120% text-indent: 0cm text-justify: kashida text-kashida: 0%"><a name="OLE_LINK117"></a><a name="OLE_LINK116"><span style="mso-bookmark: OLE_LINK117"><font face="Times New Roman" size="3">The main goal of this study was to examine the use of cyanobacteria </font></span></a><font face="Times New Roman"><font size="3">for evaluating the quality of running water. Accordingly epilithic cyanobacterial communities were collected in Dez River and Ojeyreb drain in south of Iran. Samples were collected in two seasons: autumn and spring. Effective physical and chemical factors on the structure of cyanobacterial communities and the dispersion of the species in relation with them were determined using PCA and CCA analyses. The Shannon-wiener biodiversity index was used to define the species diversity. The concentration of Nitrate as main nutrient had significant increase in Drain stations. A decline in species richness was observed associated with these increases in nutrient load in both seasons in different cyanobacterial community structure. <span style="mso-spacerun: yes"> </span>The results indicated that order Oscillatoriales had higher proportion of cyanobacteria species at Drain. <font size="2">The <span style="color: black">species <i>Oscillatoria chlorina</i>, <i>Chroococcus minor</i>,</span> <i><span style="color: black">Phormidium tenue</span></i><span style="color: black"> </span>and <i><span style="color: black">Lyngbya kuetzingii</span></i><span style="color: black"> S</span></font> had the most positive correlation with nutrient factor. <span style="color: black">Species <i>Lyngbya infixa</i></span> and <i><span style="color: black">Lyngbya</span><span style="color: rgb(0, 176, 240)"> </span><span style="color: black">mesotrichia</span></i><span style="color: black"> </span></font><font size="3">had the most negative correlation with nitrate. Our results confirm the using of cyanobacteria species as indicators for monitoring eutrophication in rivers and define them as water eutrophication bioindicators. </font></font></p><font face="Times New Roman" size="3"> </font> Cyanobacteria, Drainage, Eutrophication, River, Water quality, PCA 876 891 http://jifro.ir/browse.php?a_code=A-10-1-206&slc_lang=en&sid=1 N. Soltani 10031947532846004763 10031947532846004763 No K. Khodaei khodaeekamal@yahoo.com 10031947532846004764 10031947532846004764 Yes N. Alnajar 10031947532846004765 10031947532846004765 No A Shahsavari 10031947532846004766 10031947532846004766 No A. Ashja Ardalan 10031947532846004767 10031947532846004767 No