Stations in the USGS's National Stream Quality Accounting Network (NASQAN)

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.

United States
Water quality
Surface water

本数据集为美国地质调查局（U.S. Geological Survey）国家河流质量核算网络（National Stream Quality Accounting Network，简称NASQAN）的监测站点点位覆盖数据。NASQAN始建于1973年，目前其站点的水质数据采集周期分为双月与季度两类。但自1992年起，部分双月监测站点的采样频次将调整为每年仅5次。
数据集针对美国本土、阿拉斯加、夏威夷/关岛以及波多黎各分别提供独立的覆盖数据，旨在囊括截至1992年春季该网络内所有已运行或曾运行的监测站点（部分站点现已停用或终止监测）。
覆盖区域：美国；数据主题：水质、地表水