<![CDATA[Graphical Abstract Highlight Research First study to analyze the three-year spatiotemporal distribution of nitrate and phosphate in the Serayu River Basin. Reveals seasonal and spatial nutrient hotspots linked to agricultural runoff and domestic activities. Identifies strong correlations: nitrate with TSS and COD (2021), and phosphate with COD (2021–2022) and pH (2023). Supports integrated watershed management through evidence-based nutrient pollution assessment using PCA and spatial mapping. Abstract The Serayu Watershed is a vital area in Indonesia, where agricultural runoff contributes to nutrient enrichment in rivers. This study offers novelty as it is the first to analyze the spatiotemporal distribution of nitrate and phosphate in the Serayu River over a three-year period (2021–2023). The research aims to support sustainable watershed management by examining nutrient dynamics and their correlation with environmental parameters such as dissolved oxygen (DO), pH, total suspended solids (TSS), and chemical oxygen demand (COD). Water sampling was conducted at 15 stations across upstream, midstream, and downstream segments. Data were analyzed using Microsoft Excel and PAST 4.03, applying Principal Component Analysis (PCA) and biplot methods. Results showed nitrate levels were highest downstream in 2021, but shifted upstream in 2022–2023, likely due to organic matter decomposition. Phosphate remained highest midstream throughout the period, linked to domestic activity and land use. Nitrate levels fluctuated seasonally, especially during the rainy season, while phosphate levels were relatively stable. Spatial mapping highlighted dynamic nitrate changes in Banjarnegara and Cilacap, with phosphate distribution remaining more uniform. Correlation analysis revealed nitrate was related to TSS and COD in 2021, had no significant correlation in 2022, and was linked with pH in 2023. Phosphate consistently correlated with COD and pH. These findings emphasize that both natural and human-induced factors drive nutrient variability in the Serayu watershed, underlining the urgency of integrated watershed management to control nutrient pollution and protect water quality.]]>
