Downstream of Sungai Batu Ferringhi is connected to the popular tourism spot of Batu Ferringhi Beach in Malaysia. The water quality deterioration in Sungai Batu Ferringhi directly affects the seawater quality, subsequently impacting fisheries and tourism activities. This study aims to identify both point and diffuse pollution sources in Sungai Batu Ferringhi and simulate water quality during normal flow and low flow events using QUAL2K. Concentrations of biochemical oxygen demand (BOD), ammoniacal nitrogen (NH3-N), total suspended solids (TSS), and total phosphorus are the focal water quality parameters. 6 water quality stations and 2 point sources were identified, and samples were collected from each. As per the National Water Quality Standards (NWQS), Sungai Batu Ferringhi falls under Class III. The baseline model was initially simulated and calibrated using a trial-and-error method. A 7Q10 low flow event was simulated by modifying water flow. During both normal flow and 7Q10 low flow events, most upper and middle stream sections of Sungai Batu Ferringhi met Class III standards, except for total phosphorus concentration. However, certain water quality parameters like BOD and total phosphorus failed to meet Class III standards, particularly in the middle and lower stream sections during both flow scenarios. A noticeable increase in BOD and total phosphate concentrations in the middle stream during low flow events impacted the river’s water quality. Both point sources had negligible impacts on Sungai Batu Ferringhi’s water quality. Diffuse sources, potentially from forest runoff, urban runoff, and agricultural runoff, are identified as the primary contributors of pollutants to Sungai Batu Ferringhi.