This map is provided by the US Census Tiger Mapping Server.
Another interface to this service is provided by USGS Mapping Information server.
For your searching convenience the master list of stations has been updated with about 3000 new stations. This means that stations which only have Peakflow data (but not Historical Daily Values) will now appear when you search for a station whereas before only stations with Historical Daily Values data would appear.
Please be sure that you always access NWIS-W via water.usgs.gov.
This page was created in real time by the NWIS-W package: ( NWIS-W: 3.01pr ; API: 3.0pr ; nmdmap: 3.0pr )