Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 15 6 2023 11 20 788 795 Olorunjuwon Bello Department of Microbiology, Faculty of Science, University of Medical Sciences, Ondo, Ondo State, Nigeria Bridget Akinpeloye Department of Microbiology, Faculty of Science, University of Medical Sciences, Ondo, Ondo State, Nigeria Temitope Bello Department of Biological Sciences, Faculty of Basic and Applied Sciences, Elizade University, Ilara-Mokin, Ondo State, Nigeri Yinka Oluwafemi Department of Microbiology, Faculty of Science, University of Medical Sciences, Ondo, Ondo State, Nigeria Bamikole Osungbemiro Department of Chemistry, Faculty of Science, University of Medical Sciences, Ondo, Ondo State, Nigeria 2022 12 09 2023 02 25 Background and Objectives: Water is crucial to human existence but may be contaminated with microorganisms, thus making it unfit for consumption. This study aimed to evaluate the physicochemical properties and bacterial loads of selected river waters in Ondo State, Nigeria. Materials and Methods: Ten major rivers were sampled between April and August, 2021. The pH, temperature, total alkalinity, colour, turbidity, electrical conductivity, dissolved oxygen, ammonium, aluminium, organic matters, nitrate levels including the microbial loads were determined according to standard procedures. Confirmation of identified isolates was achieved by API 20E and API 20NE. Results: The turbidity, colour, conductivity, ammonium, and aluminium ranged from 4.3 to 15.2 NTU, 4 to 20 NTU, 123.5 to 580.2 mgL-1, 0 to 3.5 mgL-1, and 0.05 to 1.7, respectively. Most physicochemical parameters showed no significant differences from the WHO permissible limits for drinking water (p > 0.05). The total viable bacterial count in the rivers ranged from 1.5 × 105 to 6.3 × 105 CFUmL-1, while the total coliform count ranged from 1.3 × 103 to 4.8 × 103 CFUmL-1. The predominant bacteria were Escherichia coli and Pseudomonas aeruginosa. Conclusion: This study revealed that the physiochemical properties of the waters were majorly within the WHO permissible standards but with significantly higher bacterial loads. https://ijm.tums.ac.ir/index.php/ijm/article/view/4035 https://ijm.tums.ac.ir/index.php/ijm/article/download/4035/1626