Acid sulfate soils present significant challenges for agricultural utilization due to their high acidity and toxic levels of dissolved iron triggered by pyrite oxidation. This study aimed to investigate the hydrological influence of the Nagara River on electrical conductivity (EC), sulfate, and dissolved iron contents in the soil and water of acid sulfate soil in Tapin Regency, South Kalimantan. Soil an d water samples were collected using a purposive sampling method at two distances from the river: Sungai Puting Village (0.2 km, Typology A) and Pandahan Village (20 km, Typology D). The data were analyze using the independent t-test to determine differences between the two locations. The results indicated that EC water was significantly higher in Sungai Puting (126.55 μS cm?¹) compared to Pandahan (45.01 μS cm?¹), although both remained within the low conductivity category. In contrast, water pH (averaging 5.91 and 5.85) and dissolved iron in water (averaging 0.81 ppm and 0.64 ppm) did not differ significantly between the two sites. For soil characteristics, soil electrical conductivity and soil sulfate levels showed no significant differences, with sulfate reaching very high concentrations in both villages. However, dissolved iron in the soil showed a highly significant difference, where Sungai Puting exhibited a drastically higher concentration (627.67 ppm) than Pandahan (119.01 ppm), both falling into the very high risk category. In conclusion, closer proximity to the Nagara River hydrologically correlates with increased electrical conductivity in water and higher dissolved iron accumulation in the soil, which necessitates proper water management and liming interventions to support sustainable rice cultivation.