en تخصصي Special Original articles <strong><em>Introduction:</em></strong> Microbial contamination prediction through detecting the indicator bacteria in natural waters is the first health and environmental step for preventing the transmission of water-associated diseases. This study was designed to determine the correlation between <em>Escherichia coli</em> as the indicator bacterium, on the one hand, and <em>Salmonella </em>and <em>Shigella</em> Spp. As the pathogenic bacteria, on the other hand.<br> <strong><em>Materials and Methods:</em></strong> Totally, 60 natural water samples were collected from natural rivers in Gorgan during summer and autumn of 2016. In order to detect <em>Escherichia coli</em>, the membrane filter method with Endo agar and IMVIC test was used and, in order to detect <em>Salmonella</em> and Shigella, the 9-tube fermentation method and biochemical tests with selenite F medium, XLD agar, TSI, urea, and SIM were utilized. For the statistical analysis, Pearson&rsquo;s correlation test was used at the significance coefficient of < 0.05.<br> <strong><em>Results:</em></strong> Results showed that all of the analyzed bacteria were detected in the water samples. The frequency of <em>Salmonella</em>, <em>Shigella</em>, <em>Escherichia coli</em>, <em>Klebsiella</em>-<em>Enterobacter,</em> and <em>Citrobacter</em> was 9.5, 22.2, 4.8, 22.2, and 65.1%, respectively. The statistical analysis demonstrated no statistical correlation between <em>Escherichia coli,</em> on the one hand, and <em>Salmonella</em> and <em>Shigella,</em> on the other hand; but the relationship between <em>Salmonella</em> and <em>Shigella</em> was significant.<br> <strong><em>Conclusion:</em> </strong>Judging the microbial quality of water supplies cannot be sufficient only based on the presence or absence of <em>Escherichia coli</em> bacterium. Therefore, that the use of other secondary indicator bacteria such as fecal streptococci and supplementary sulphite-reducing clostridia will be advised. Escherichia Coli, Salmonella, Shigella, Water Pollutions, Rivers. 416 421 http://jehsd.ssu.ac.ir/browse.php?a_code=A-10-1-65&slc_lang=en&sid=1 Ali Shahryari No Environmental Health Research Center, Golestan University of Medical Sciences, Gorgan, Iran. Rahim Aali No Health Technology Incubator Center, Urmia University of Medical Sciences, Urmia, Iran. Mohammad Reza Zare No Ewaz School of Health, Larestan School of Medical Sciences, Ewaz, Iran. Reza Ghanbari Yes Social Determinants of Health Research Center, Qazvin University of Medical Sciences, Qazvin, Iran.