Abstract—This study was conducted to assess surface water quality at Bung Binh Thien reservoir, An Giang province, Vietnam. Sixty inhabitants living around the reservoir were interviewed to identify pollution sources. Nine water samples were collected in the dry and rainy seasons and then analyzed for eighteen variables (temperature, pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), turbidity (Turb), dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), sulfate (SO₄²⁻), chloride (Cl⁻), ammonia (NH4+-N), nitrate (NO3--N), total nitrogen (TN), orthophosphate (PO43--P), total phosphorus (TP), and coliform). Principal component analysis (PCA) was used to identify the primary parameters influencing water quality. The results indicated that the major concerns for water quality in the reservoir were suspended solids, organic matters and fecal microbes. There were significant seasonal variations in water quality. While organic pollution was mainly observed in the dry season, the microbial problem was recorded in the rainy season. This pollution was associated with domestic wastes, agricultural production, livestock, and aquaculture. The PCA results also revealed that DO, BOD, COD, N-NH₄⁺, N-NO₃⁻, P-PO₄³⁻, TP, Cl⁻, and coliform greatly influenced water quality variations, thus requiring these parameters in the monitoring program. The local authority should apply proper measures to improve water quality in the reservoir, and inhabitants should not directly use water for their domestic activities without adequate treatment.