Post-normalization Water Quality Assessment of the Karang Mumus River Based on Physicochemical, Microbiological Parameters, and the STORET Index

River normalization has been widely implemented as a structural approach to restore urban rivers; however, its effectiveness in improving water quality remains uncertain. This study assessed post-normalization water quality of the Karang Mumus River (KMR), an urban river in Samarinda, Indonesia, based on physicochemical parameters (TSS, TDS, pH, DO, BOD, COD, nitrate, nitrite, and Pb) and microbiological indicators (Fecal Coliform). Water quality status was determined using the STORET index in accordance with Indonesian Government Regulation No. 22/2021 for Class II surface waters. Water samples were collected purposively at six stations representing upstream, midstream, and downstream segments. The results showed significant improvements in physical and microbiological parameters, as indicated by a reduction in TSS from 40–251 mg/L to 14–83 mg/L, an increase in DO from 1.3–4.0 mg/L to 3.6–4.2 mg/L, and a marked decrease in Fecal Coliform from 1.5×10⁶ to 150–230 MPN/100 mL. In contrast, nitrite and Pb concentrations consistently exceeded regulatory limits. STORET scores classified the river as slightly to moderately polluted, indicating an improvement compared to pre-normalization conditions. These findings demonstrate that river normalization effectively enhances physical and microbiological water quality but remains insufficient to control dominant chemical pollutants derived from urban activities.