This data release contains daily time series estimates of natural streamflow at the outlets of more than 80,000 12-digit hydrologic units in 19 study regions across the conterminous U.S. from October 1, 1980 through September 30, 2017, using three statistical techniques: Nearest-Neighbor Drainage Area Ratio (NNDAR), Map-Correlation Drainage Area Ratio (MCDAR), and Ordinary Kriging of the logarithms of discharge per unit area (OKDAR). Location information and drainage areas for index gages were obtained from the "Reference" gages of the GAGES-II dataset (Falcone, 2011, https://water.usgs.gov/lookup/getspatial?gagesII_Sept2011); location information and drainage areas for the HUC12 outlets were derived from attributes of the NHDPlus Version 2.1 (Price, 2016; Wieczorek and others, 2018). Daily streamflow data for index gages were retrieved from the National Water Information System (NWIS) on September 7, 2018. NNDAR and MCDAR estimates were computed following methods described by Farmer and others (2014). OKDAR estimates were computed using pooled variograms for each study region following methods described by Farmer (2016). The three sets of streamflow estimates represent expected natural streamflow conditions with minimal disturbance by human activities, in other words, without the effects of regulation, diversion, mining, or other anthropogenic activities.