Monsoon-induced rainfall and runoff significantly alter river water quality by introducing sediments, nutrients, and pollutants, impacting aquatic ecosystems and human use. This study evaluates the Dhamodar River’s water quality during the monsoon season across seven stations (DC-1 to DC-7), focusing on physicochemical parameters and sub-indices. Parameters analyzed included pH, EC, TDS, turbidity, DO, BOD, COD, TSS, nitrate, nitrite, ammonia, phosphate, sulfate, chloride, TOC, alkalinity, and hardness. Sub-indices (( qi )) were calculated using (qi=(Ci÷Si)×100), where ( Ci ) is the measured concentration and ( Si ) is the regulatory standard, to assess compliance. Data, visualized in bar plots (Figures 1 and 3), radar plots (Figures2 and 5), and a line plot (Figure 4), revealed significant spatial and temporal variations. Turbidity peaked at DC- 5 (11.5 NTU), with TSS reaching 81 mg/L, indicating heavy sediment load from runoff. EC (1200 μS/cm) and TDS (780 mg/L) were highest at DC-7, reflecting ionic inputs from urban or industrial sources. BOD (4.0 mg/L) and COD (25 mg/L) at DC-7 suggested elevated organic pollution, while nutrient levels, particularly nitrate (32.5 mg/L) and phosphate (0.84 mg/L) at DC-5, pointed to agricultural runoff. Sub-indices highlighted severe pollution, with turbidity (230.00 at DC-5) and COD (250.00 at DC-7) indicating significant deviations from standards. Figures 1 and 2 showed how dilution and silt altered parameters, while Figures 3–5 underscored site-specific impacts, with DC-5 and DC-7 most affected. These findings emphasize the monsoon’s role in exacerbating water quality degradation through sediment and pollutant transport, highlighting the need for targeted management strategies to mitigate runoff impacts in the Dhamodar River basin.