Water quality sites indexed to NHDPlus v2.1 flowlines for the 2012 and the 2017 periods of the U.S. Geological Survey's Surface Water Status and Trends project

This data release provides a list of 2,304 water-quality sampling sites indexed to NHDPlus v2.1 flowlines along with the verified ComIDs. ComIDs are the unique identifiers for NHDPlus flowlines and allow the sites to be joined to ancillary and watershed information from other sources published for that purpose. The sites include those assembled for the period 1972-2012 by the U.S. Geological Survey Surface Water Status and Trends project of the National Water-Quality Program (Oelsner and others, 2017, https://doi.org/10.3133/sir20175006), as well as additional water-quality sites assembled for the 2013-2017 time period. Land cover information from the National Land Cover Dataset for the period 2001 through 2016 is also provided for the watershed of each site in this data release.