River water quality assessment is essential for sustaining aquatic ecosystems and supporting sustainable water use, particularly in irrigation rivers influenced by mixed land use activities. This study evaluated the water quality status of Sungai Besar, Tunjang through the Terusan Utara in Jitra, Kedah, using physicochemical parameters and the Malaysian Water Quality Index framework. Water samples were collected from three sampling stations over a three-month period from June to August using the grab sampling method. Parameters analysed included pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, ammoniacal nitrogen and total suspended solids. Measured values were compared with the National Water Quality Standards of Malaysia and integrated into Water Quality Index calculations. The results showed clear variation in water quality along the river. Stations 1 and 3 exhibited good water quality, with most parameters classified within Class I and Class II and Water Quality Index values ranging from 88.81 to 96.47. In contrast, Station 2 showed significant degradation, with biochemical oxygen demand and chemical oxygen demand values reaching 77.5 mg/L and 295 mg/L, respectively, resulting in polluted to slightly polluted Water Quality Index classifications ranging from 44.54 to 71.57. Elevated ammoniacal nitrogen and episodic increases in suspended solids further indicated substantial organic and chemical pollution. Overall, this study provides updated baseline data for irrigation rivers in northern Kedah and supports site-specific river management and sustainable agricultural water use.

Abstract

River water quality assessment is essential for sustaining aquatic ecosystems and supporting sustainable water use, particularly in irrigation rivers influenced by mixed land use activities. This study evaluated the water quality status of Sungai Besar, Tunjang through the Terusan Utara in Jitra, Kedah, using physicochemical parameters and the Malaysian Water Quality Index framework. Water samples were collected from three sampling stations over a three-month period from June to August using the grab sampling method. Parameters analysed included pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, ammoniacal nitrogen and total suspended solids. Measured values were compared with the National Water Quality Standards of Malaysia and integrated into Water Quality Index calculations. The results showed clear variation in water quality along the river. Stations 1 and 3 exhibited good water quality, with most parameters classified within Class I and Class II and Water Quality Index values ranging from 88.81 to 96.47. In contrast, Station 2 showed significant degradation, with biochemical oxygen demand and chemical oxygen demand values reaching 77.5 mg/L and 295 mg/L, respectively, resulting in polluted to slightly polluted Water Quality Index classifications ranging from 44.54 to 71.57. Elevated ammoniacal nitrogen and episodic increases in suspended solids further indicated substantial organic and chemical pollution. Overall, this study provides updated baseline data for irrigation rivers in northern Kedah and supports site-specific river management and sustainable agricultural water use.