Zoning of aquaculture water quality in Cau Hai lagoon was conducted by comparing with the national standards (QCVN02-19:2014/BNNPTNT, QCVN08-MT:2015/BTNMT, and QCVN38:2011/BTNMT) through the help of GIS. Temperature, dissolved oxygen (DO), nitrate parameters were suitable to aquaculture activities. One hundred percent of the area had pH values in suitable range for aquaculture in the dry season, whereas only 79.4% was in the rainy season. Salinities were most in suitable range for shrimp

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... . The alkalinity was unsuitable for aquaculture in rainy season and dry season was respectively 88.04% and 28.92%. BOD 5 levels exceeded the QCVN08-MT:2015/BTNMT standard. Phosphate contents were not suitable for aquaculture with 91.13% and 53.57% of the areas the rainy season and dry season, respectively. Un-ionized ammonia concentrations exceeded the standard, with 41.68% and 36.55% of the areas in rainy season and dry season, respectively. The concentrations of total coliform were higher than the standard with 63.33% of the areas in rainy season and 44.19% in the dry season.