Rivers entering the lake constitute the primary pathways for external nutrient inputs, and variations in nitrogen (N) and phosphorus (P) fluxes directly influence lake eutrophication and the risk of algal blooms. To accurately assess the pollutant export characteristics and driving mechanisms of typical inflow rivers in the Chaohu Basin, this study focuses on the Hangbu River, the largest tributary discharging into Chaohu Lake. Using the period-average flux method, the Load Estimator (LOADEST) model, and the WRTDS model, fluxes and long-term trends were estimated for hydrological and water-quality data from 2019 to 2024 at four stations along the river: Yaojiahe (upstream), Hekou Bridge (midstream), Sanhe Town Bridge (mid-downstream), and Beizhadukou (downstream). The period-average method is computationally simple but produces large errors. In comparison, the LOADEST model performs better in the Chaohu Basin and achieves substantially higher agreement with observed daily fluxes than the WRTDS model. The results show that LOADEST performs best under conditions of continuous discharge records and relatively sparse water-quality measurements, with R2 values of 0.89 to 0.97 and NSE values of 0.84 to 0.98, allowing stable reconstruction of continuous flux series. Based on LOADEST, the estimated total nitrogen (TN) and total phosphorus (TP) fluxes exhibit strong temporal and spatial variability. At the lake-inlet section, the wet season from May to September contributes 68 to 77 percent of annual TN flux and 72 to 81 percent of annual TP flux. A single storm event with 61.8 mm of rainfall can generate as much as 73 percent of the monthly flux, revealing a pronounced pulse-like export pattern. Spatially, TN and TP fluxes increase progressively from upstream to downstream, and the annual fluxes at the Beizhadukou section reach 4.24×106 kg N per year and 2.25×105 kg P per year, which are 10 to 17 times higher than those upstream. Trend decomposition indicates that TN flux into the lake has continued to rise over the past five years, whereas TP flux shows a slight decline, suggesting persistent nitrogen accumulation but a temporary easing of phosphorus export. Overall, flux variations are jointly driven by hydrological processes and human activities. Intense rainfall events amplify the contributions of agricultural and urban pollution to nutrient loading at downstream sections. These findings provide scientific support for external load assessment, pollution control, and algal bloom risk management in the Chaohu Basin under current environmental conditions.