This is a point coverage of stations in the U.S. Geological Survey's National Stream Quality Accounting Network (NASQAN). NASQAN was established in 1973. Water-quality data currently is collected at NASQAN sites on bimonthly and quarterly intervals. However, some of the bimonthly stations will be sampled only five times a year beginning in 1992. Separate coverages exist for the conterminous United States, Alaska, Hawaii/Guam, and Puerto Rico. The coverages attempt to represent all of the stations that are or have been in the network (some are inactive or discontinued) as of spring 1992.
Additional publication details
USGS Unnumbered Series
Stations in the USGS's National Stream Quality Accounting Network (NASQAN)