Water Quality Status of the Sanga-Sanga River, East Kalimantan, determined with the Pollution Index Method under high- and low-tide conditions

Abstract

The Sanga-Sanga River in the Mahakam Delta region of East Kalimantan supplies raw water and supports bathing, washing, transport and fishing for nearby communities, yet it also receives inputs from riverbank settlements and from mining-related industry. This study assessed the river’s water quality status with the Pollution Index (PI) method of State Minister of Environment Decree No. 115 of 2003, using the Class I–IV standards of Government Regulation No. 22 of 2021 as references. Water was sampled in four replicates at high tide and at low tide at three stations (upstream, middle and downstream) between November 2024 and January 2025. Chemical oxygen demand (COD), lead (Pb) and copper (Cu) exceeded the standards: COD ranged from 12.7 to 35.1 mg/L, mean Pb from 0.22 to 0.35 mg/L, and mean Cu reached 0.10 mg/L at low tide. At high tide, PI values were 2.89, 1.66, 1.28 and 0.93 for Classes I to IV, so the river was lightly polluted for Classes I–III and met the Class IV standard. At low tide, PI values were 3.02, 1.76, 1.72 and 1.71, and the river was lightly polluted for all four classes. Low-tide PI exceeded high-tide PI for every class, and the difference grew from about 4% for Class I to about 84% for Class IV. The Sanga-Sanga River therefore does not meet the Class I standard for raw drinking water, and its status depends on the tidal phase at the time of sampling. Tidal dilution is the most plausible explanation for the better high-tide condition, but this remains to be tested with salinity and discharge data. Source control of domestic and industrial effluents and monitoring at both tidal phases are recommended.