This data release includes concentrations of 24 per- and polyfluoroalkyl substances (PFAS) and physical properties of water-quality samples collected by the U.S. Geological Survey (USGS) at 64 selected sites in rivers and streams in Massachusetts over three rounds of sampling. The samples were collected from August to November 2020 when streamflow conditions were below normal (also considered to be base-flow conditions) at rivers and streams in urban areas that receive treated wastewater from municipal wastewater-treatment facilities, and in rural rivers and streams that are not associated with municipal wastewater discharges and may have other source inputs of PFAS. The measured physical properties include water temperature, specific conductance, pH, dissolved oxygen, and turbidity and the quality-control data from blanks, replicates, laboratory control samples, and laboratory spike samples are provided. The physical properties, along with all of the discrete water-quality PFAS data, except the quality-control data, are also available online from the U.S. Geological Survey's National Water Information System (NWIS) database (https://nwis.waterdata.usgs.gov/nwis). This data release is structured as a set of tab-delimited (.txt) files.The metadata includes descriptions of files: Site_Information.txt, Abbreviations_and_Remark_Codes.txt, and Analysis_Information.txt. This data release also includes a Data Dictionary (Data_Dictionary.txt) that is used to describe environmental sample data (Environmental_Data.txt), and Quality Control field and laboratory blank data (QC_Blanks.txt), field and laboratory replicate data (QC_Replicates.txt), and laboratory control sample and spike data (QC_Laboratory_Control_Samples_and_Spikes.txt).