This map from the United States Geological Survey (USGS) provides real-time data of streamflow conditions as measured at USGS gauging stations around the country. By selecting areas within a state on the map, users receive daily provisional data (which may be subject to revision) on current conditions and flood thresh-holds, as well as streamflow, stage, and rainfall graphs. Historic data and...

The US Geological Survey describes the location, extent, and geologic and hydrologic characteristics of major aquifers in the United States in the Groundwater Atlas of the United States Website. The groundwater resources of the US are broken down into specific regions, which are described in chapters. Some of the chapters are not available online, but the chapters that are available include...

The Oceanographic Products and Services Division (OPSD) of the National Oceanic and Atmospheric Administration (NOAA) "collects, analyzes and distributes historical and real-time observations and predictions of water levels, coastal currents and other meteorological and oceanographic data." This wonderful site explains the science behind the tides and changing water levels, gives historical...