This child item includes daily mean streamflow data obtained from the U.S. Geological Survey (USGS) National Water Information System database (https://doi.org/10.5066/F7P55KJN) and subsequently used in the computation of streamflow statistics. Daily mean streamflow data for some streamgages were removed from the analyses if the daily streamflows were determined to be incorrect, estimated, or had other problems. Streamflow at each streamgage was assessed for degree of human alteration owing to dams and diversions before streamflow statistics were computed. Methods used to remove daily mean streamflows, assess alteration, and compute the summary statistics contained in this data release are described in an accompanying report (Armstrong and others, 2025). Daily mean streamflow data for the period of record at each USGS streamgage used in the analyses are grouped into 15 folders organized by the 4-digit hydrologic unit code (HUC; https://water.usgs.gov/GIS/huc.html) in which the streamgage is located. The content of these folders is described in this metadata file. A table describing characteristics of the streamgages used in the analyses is provided in text file "AtSite_Table1_StreamgageSummary.txt."