USGS WaterWatch
Display National and State maps, graphs, and tables describing real-time, recent, and past streamflow conditions for the United States including locations where floods and droughts are occurring. (Real-time data, in most cases, are transmitted once every 1 to 4 hours.) Also, you can select USGS streamgaging stations to view more detailed summary information such as hydrographs showing peak, forecast, and rating data.