fa تخصصي Special پژوهشي Research <span style="font-size:14px;"><span style="font-family:Tahoma;"><strong>Background</strong>: Today, the environmental crisis of pollution of water resources with municipal and industrial wastewater containing microplastic (MP) pollutants has become a global problem. Likewise, in Ardabil Province, Iran, municipal wastewater is discharged into the water of the River Qarasu and is the primary source of the MP pollution crisis.<br> <strong>Materials and Methods:</strong> In this descriptive cross-sectional study, the samples were taken from 5 stations in the Qarasu (Karkarq, Sarband, Anzab Sofla, Dolatabad, and Samian villages) under standard methods in 2020. The sample analysis and MP separation method were performed based on the density difference and digestion methodology. It was completed using stereo microscopy with a digital camera, fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).&nbsp;<br> <strong>Results:</strong> Studies show that WWTPs (Wastewater Treatment Plants) are the primary sources of releasing MPs into the environment. In addition to threats to water resources, MPs are consumed and digested by aquatic organisms. As a result, MPs can affect human health, the environment, and the river&rsquo;s living organisms.<br> <strong>Conclusion:</strong> The study results showed that MPs had been introduced into the River Qarasu ecosystem. MPs can have dangerous effects on the environment and living organisms and lead to an environmental crisis of water resources. Therefore, continuous river pollution monitoring is vital in the environmental crisis.</span></span><div style="text-align: right;"></div> Environmental, Waste water, Micro plastic, Water, Pollution 117 126 http://hdq.uswr.ac.ir/browse.php?a_code=A-10-406-2&slc_lang=fa&sid=1 Nouraddin Ghanbari Tapeh sepino598@gmail.com No Department of Environmental Science and Engineering, Ardabil Branch, Islamic Azad, University, Ardabil, Iran. Ebrahim Fataei eafataei@gmail.com https://orcid.org/0000-0002-9245-9796 Yes Department of Environmental Science and Engineering, Ardabil Branch, Islamic Azad, University, Ardabil, Iran. Abulfazl Naji ghanbarinoraddin3383@gmail.com No Department of Fisheries, Faculty of Marine Science and Technology, Hormozgan University, Hormozgan, Iran. Ali Akbar Imani noreddin3383@yahoo.com https://orcid.org/0000-0001-6425-4681 No Department of Agricultural Engineering, Ardabil Branch, Islamic Azad University, Ardabil, Iran. Fatemeh Nasehi karchany@yahoo.com https://orcid.org/0000-0001-8720-5081 No Department of Environmental Science and Engineering, Ardabil Branch, Islamic Azad, University, Ardabil, Iran.