L'Outil de Suivi et de Surveillance des etiages en Coherence sur le Rhone (OSSEC Rhone) est un outil permettant de caracteriser en temps reel les evenements d'etiage sur le Rhone et ses principaux affluents. OSSEC repose sur une caracterisation locale des etiages a partir d'un seuil, puis sur la mise en coherence des etiages locaux au sein d'une plus grande zone spatiale. Cette methode a ete adaptee au cas du bassin versant rhodanien, qui possede des donnees anthropisees et une dependance amont-aval. Cette caracterisation permet d'obtenir, pour chaque station hydrologique, les dates de debut, de fin, et la severite de chaque etiage, en coherence sur l'ensemble du bassin du Rhone. Lance en temps reel, OSSEC Rhone recupere les dernieres donnees de debit acquises et lance la methodologie depuis le dernier evenement caracterise. L'outil compare ensuite l'evenement en cours avec un historique d'evenements deja sauvegarde. Des figures sont generees puis selectionnees par l'operateur afin d'etablir la chronologie et l'evolution de l'evenement en cours. OSSEC Rhone permet d'approfondir les connaissances des etiages, en les caracterisant de facon plus complete que de simples statistiques de debit. Les evenements obtenus etant spatialement coherents, il est alors possible d'etudier leur evolution saisonniere ou leur frequence. OSSEC Rhone is a tool for monitoring and characterising low-flow events on the Rhone River and its tributaries in real time. Based on daily streamflow series, low-flow events are characterised for each hydrological station, by a threshold method. This method provides a beginning and ending date, as well as the severity of each identified event. Then, based on an overlapping of dates, events are spatially matched across stations to identify spatio-temporal events on the Rhone tributaries. Lastly, these are matched to the events identified on the Rhone River. These three steps ensure consistency between low-flow events of the main river and of its tributaries. In real time, OSSEC retrieves streamflow data and launches the methodology since the last characterized event in the archive. It can then determine whether a low-flow event is currently underway, and its inception date, duration, and severity. The selected event is then compared to other historical events. OSSEC Rhone makes it possible to deepen the knowledge of such events by going beyond simple streamflow statistics, usually computed at the monthly scale. OSSEC Rhone is therefore a decision-making tool for water managers, allowing a day-by-day assessment of the spatial evolution of a low-flow event throughout a year.