Surface-water-quality data were collected from the lower Kansas River Basin in Kansas and Nebraska. The data are presented in 17 tables consisting of physical properties, concentrations of dissolved solids and major ions, dissolved and total nutrients, dissolved and total major metals and trace elements, radioactivity, organic carbon, pesticides and other synthetic-organic compounds, bacteria and chlorophyll-a, in water; particle-size distributions and concentrations of major metals and trace elements in suspended and streambed sediment; and concentrations of synthetic-organic compounds in streambed sediment. The data are grouped within each table by sampling sites, arranged in downstream order. Ninety-one sites were sampled in the study area. These sampling sites are classified in three, non-exclusive categories (fixed, synoptic, and miscellaneous sites) on the basis of sampling frequency and location. Sampling sites are presented on a plate and in 3 tables, cross-referenced by downstream order, alphabetical order, U.S. Geological Survey identification number, sampling-site classification category, and types of analyses performed at each site. The methods used to collect, analyze, and verify the accuracy of the data also are presented.