The dynamics of total phosphorus (TP) concentrations in shallow lakes are collectively driven by multiple environmental factors. The complexity of these underlying mechanisms is closely related to the lake"s physicochemical properties. Based on high-frequency data from national water quality, hydrological, and meteorological monitoring stations in the Lake Chaohu basin from 2021 to 2024, this study employed principal component analysis (PCA) and time-lag correlation analysis to elucidate the variation patterns of TP concentrations, identify the primary driving factors, and determine the risk threshold grades of environmental factors associated with TP exceedance or abrupt changes. The results indicated that water temperature (WT), dissolved oxygen (DO), and algal density (AD) were the dominant environmental drivers governing TP fluctuations in Lake Chaohu, with a cumulative contribution rate exceeding 50%. Wind speed (WD) was identified as a key meteorological factor. Furthermore, this study identified a cascading driving process of TP dynamics with distinct time-lag effects in Lake Chaohu. Specifically, a rise in WT during summer was followed by an increase in algal biomass after 4 days, accompanied by a significant decline in DO. The decrease in DO rapidly induced an elevation in water TP concentration within 24 hours, indicating a rapid response of phosphorus release at the sediment-water microinterface. The peak impact of AD on TP concentration occurred with a 3-day lag, attributable to both direct phosphorus release during algal growth and senescence, and indirect effects via DO consumption. Based on these findings, risk threshold grades for DO (7.69, 7.08, 6.72 mg/L) and AD (9.80, 15.64, 21.14 × 10? cells/L) were established for different TP concentration intervals in Lake Chaohu: (0.05, 0.075], (0.075, 0.1], and >0.1 mg/L. These results provide a crucial temporal decision-making basis for TP risk early warning and precision management in Lake Chaohu.