A system and method for generating synthetic streamflow data for a malfunctioning streamgage is provided. The method uses both classification and regression techniques to accurately predict streamflow data for the malfunctioning streamgage based on measured streamflow data from other streamgages and based on correlations between the streamgages. The system and method may also provide a method of improved flood forecasting, by updating flood forecasts using synthetic streamflow data when measured streamflow data from one or more streamgages are unavailable. The system may generate flood forecast information and/or flood warning messages.