Assessment of water quality in the main canal systems in Ho Chi Minh City, Vietnam

This study evaluated the surface water quality of five major urban canal systems, including Tham Luong – Ben Cat – Vam Thuat, Nhieu Loc – Thi Nghe, Tau Hu – Ben Nghe, Doi – Te, and Tan Hoa – Lo Gom, under high and low tides at 40 sampling sites. The results revealed severe organic and nutrient pollution, with COD and NH 4 + -N concentrations reaching up to 157 mg/L and 21 mg/L, respectively, far exceeding the National Technical Regulation on Surface Water Quality (QCVN 08:2023/BTNMT). DO levels were critically low (<1.0 mg/L) at several locations, while total coliform concentrations exceeded regulatory limits by more than 20 times. Water quality assessment using the Vietnam Water Quality Index (VN-WQI) classified all canals as heavily polluted to poor quality, with WQI values ranging from 12.12 to 62.17. Pollutant concentrations were generally higher during low tide, whereas high tide promoted partial dilution and improved WQI values at several locations. These results indicate that elevated organic and nutrient loads from untreated wastewater intensify oxygen depletion and microbial contamination under low-tide conditions, while tidal flushing during high tide enhances dilution and short-term water quality recovery, providing mechanistic insight into the role of hydrodynamics in urban canal pollution. • Main canals in Ho Chi Minh City have a low Water Quality Index (WQI < 30). • Organic matter and nutrients contents in canal water have not met the standard discharge. • Coliform contamination (6,600 – 93,000 CFU/100mL) is a serious concern in canal water.