Water stable isotope data measured on water chemistry samples collected as part of the National Aquatic Resource Surveys (NARS). One file is for the National Rivers and Streams Assessment (NRSA), and contains the data collected in 2008-2009, 2013-2014, and 2018-2019. The other file is for the National Lakes Assessment (NLA) and contains the water isotope data, as well as evaporation to inflow and water residence time calculated from the water isotope data from samples collected in 2007, 2012, and 2017. More data about these sites can be obtained from the EPA NARS website: https://www.epa.gov/national-aquatic-resource-surveys/data-national-aquatic-resource-surveys.

This dataset is associated with the following publication: Putman, A., P. Longley, M. McDonnell, J. Reddy, M. Katoski, O. Miller, and J. Brooks. Isotopic evaluation of the National Water Model reveals missing agricultural irrigation contributions to streamflow across the western United States. HYDROLOGY AND EARTH SYSTEM SCIENCES. EGS, 28(13): 2895–2918, (2024).