<p>This study examines the influence of the El Niño–Southern Oscillation on the statistical distribution of daily inflows to the 15 most important hydropower reservoirs across Colombia over the period 2000–2024. Twenty-five years of daily streamflow data were analyzed to determine whether El Niño–Southern Oscillation phases (La Niña, Normal, El Niño) produce statistically distinct hydrological signatures. Using the <i>Oceanic Niño Index</i> to classify each month into one of the three El Niño–Southern Oscillation phases, daily inflow records were grouped accordingly and applied the Anderson–Darling test to evaluate statistical differences among distributions. The analysis was performed independently for each river and calendar month, resulting in 540 pairwise comparisons. Six of eight possible outcome patterns were observed, with the most frequent pattern–rejection of the null hypothesis in all three comparisons–occurring in nearly 70% of the 180 river-month cases, indicating strong phase-dependent hydrological differentiation. The results exhibit clear spatial and temporal variability in El Niño–Southern Oscillation influence, with strongest signals during December–March and considerable complementarity among major reservoirs. By comparing monthly and daily streamflow statistics, the analysis demonstrates that daily resolution provides richer and more operationally relevant information, especially for reservoir management. These findings highlight the value of incorporating El Niño–Southern Oscillation-phase-resolved diagnostics into water resources planning and energy system operations in tropical regions influenced by climate variability.</p>