Jointly managed by multiple states and the federal government, there are many ongoing efforts to characterize and understand water quality in the Delaware River Basin (DRB). Many State, Federal and non-profit organizations have collected surface-water-quality samples across the DRB for decades and many of these data are available through the National Water Quality Monitoring Council's Water Quality Portal (WQP). In this data release, WQP data in the DRB were harmonized, meaning that they were processed to create a clean and readily usable dataset. This harmonization processing included the synthesis of parameter names and fractions, the condensation of remarks and other data qualifiers, the resolution of duplicate records, an initial quality control check of the data, and other processing steps described in the metadata. This data set provides harmonized discrete multisource surface-water-quality data pulled from the WQP for nutrients, sediment, salinity, major ions, bacteria, temperature, dissolved oxygen, pH, and turbidity in the DRB, for all available years.