Abstract India has an extensive network of reservoirs, yet their influence on streamflow extremes remains poorly quantified. To understand how reservoirs have altered the natural flow regime across India, we integrate 223 reservoirs into a national hydrologic modeling system integrating Noah‐MP land surface model and MizuRoute hydrodynamic model. Including reservoirs improved national streamflow NSE by 43%. The results reveal that reservoirs provide 46.1% median attenuation of monsoon high flow peaks and a 235% augmentation of pre‐monsoon low flows. Large reservoirs (≥1000 MCM) dominate magnitude control of extremes while smaller reservoirs (<1000 MCM) drive the 1–3 days onset lag. Alarmingly, 74% of reservoirs reach near full capacity next day immediately after a high flow peak. This systematic saturation leaves the network highly vulnerable to sequential high inflows, necessitating a shift toward forecast‐informed operations to mitigate risk.