Accurately identifying groundwater-surface water interactions along lake shorelines in arid and semi-arid regions is essential for assessing lake water quality and ecosystem health. In this study, a total of 133 water samples-including groundwater, surface water, lake water, and pore water-were collected from the irrigation area of the Hetao Basin and Ulansuhai lake to analyze typical ion concentrations, as well as stable isotopic compositions. Combined with a 222Rn mass balance model, the rates of groundwater-surface water interaction and the input fluxes of inferior-quality components along approximately 10 km of the western shoreline of Ulansuhai lake were quantified. The results indicate that Na-Cl type was the dominant hydrogeochemical type of groundwater, and the groundwater discharge rates ranged from 9.03 to 174.3 mm/d, with a mean value of 48.11 mm/d. Lacustrine groundwater discharge (LGD) displayed significant spatial heterogeneity, with the maximum rate being 19.3 times greater than the minimum. Moreover, higher discharge rates were predominantly observed along convex shoreline segments, where the average LGD rate was 2.48 times that along concave shorelines. Based on field investigations and previous studies, we infer that the spatial pattern of groundwater discharge in this area is primarily controlled heterogeneity of regional groundwater flow. The sensitivity analysis revealed that lake water 222Rn, groundwater 222Rn, and wind speed, were key drivers influencing the estimated LGD rates from the 222Rn mass balance model. This study provides new insights into the processes governing the input of inferior-quality groundwater components into large lakes in arid and semi-arid regions.