About 22 000 km of the main rivers of continental France are supervised by the French governmental service called Vigilance Crues. Despite this large supervision, many rivers are not integrated in Vigilance Crues because of their rapid response time and lack of flow measurements. In march 2017, Vigicrues opened a new service complementary to the Vigilance Crues: Vigicrues Flash. This warning service is intended for public authorities and crisis managers, who can subscribe on line . The Vigicrues Flash system assesses the risk of a flood in the next hours, with an expected anticipation close to the response time of the watershed. It relies on an event-based hydrological model developed by IRSTEA, called GRD, which is fed with radar-based rainfall. The production of the effective rainfall is distributed, while the routing is global. Two other models with daily time step initialize GRD every day. The regionalized calibration of the GRD model aims to successfully detect the exceedance of flood return period thresholds. Two return periods have been chosen for minor flood and major flood. The calculations are made on numerous strategic points along the streams with a maximum interval of 4km between two points. At each point, the discharge values corresponding to the two return periods have been estimated based on a long time series of GRD modelled discharge. In real time, calculations are updated every 15 minutes. When a threshold is exceeded, a warning is directly sent to subscribers by text message, e-mail and phone call. The subscriber is directed to the flood map (available on the website) to know precisely which streams would exceed the flood thresholds. Since the system relies on a simplified hydrological model, a selection of watersheds is necessary to meet specific requirements, like a minor influence of snow and dams, a time response over 1h30, and satisfying radar-based rainfall measurements. A first selection of eligible watersheds has been made based on the objective criteria of the SHYREG project. This selection has been reviewed by the local flood forecasting services and public authorities involved in flood management. Finally, about 30,000km of streams are eligible to Vigicrues Flash in continental France, corresponding to 10,328 eligible municipalities. After one year of operation, the users underlined that the service provided added value for flood risk mitigation.