Water-resource managers use daily mean streamflows to generate streamflow statistics and analyze streamflow condi-tions. An in-depth evaluation of flow regimes to promote instream ecological health often requires streamflow informa-tion obtainable only from a time series hydrograph. Histori-cally, it has been difficult to estimate daily mean streamflow for an ungaged location. The U.S. Geological Survey, in coop-eration with the Pennsylvania Department of Environmental Protection, Susquehanna River Basin Commission, and The Nature Conservancy, has developed the Baseline Streamflow Estimator (BaSE) to estimate baseline streamflow at a daily time scale for ungaged streams in Pennsylvania using data collected during water years 1960-2008.