This data release provides water-quality data collected and analyzed by the U.S. Geological Survey (USGS) and the Kansas Department of Health and Environment (KDHE) during 1972 through 2020. This data release includes a discrete water-quality concentration dataset (total dissolved solids, chloride, ammonia, nitrate, nitrite, nitrate plus nitrite, total Kjeldahl nitrogen, orthophosphate, total phosphorus, total suspended solids, and fecal coliform bacteria densities) used for characterization of water-quality trends in the Kansas River. This data release also includes two datasets containing annual flow-normalized and low-flow water-quality concentrations and loads (total dissolved solids, chloride, ammonia, dissolved inorganic nitrogen (computed by summing ammonia and nitrate plus nitrite), total nitrogen (computed by summing total Kjeldahl nitrogen and nitrate plus nitrite), orthophosphate, total phosphorus, total suspended solids, and fecal coliform bacteria densities), with confidence intervals, at the Kansas River at Wamego, KS (USGS station 06887500) and the Kansas River at De Soto, KS (USGS station 06892350). Annual flow-normalized and low-flow concentrations and loads were computed using the Exploration and Graphics for RivER Trends (EGRET) R package and Weighted Regressions on Time, Discharge, and Season (WRTDS) model (Hirsch and others, 2010; Hirsch and De Cicco, 2015). Confidence intervals for annual flow-normalized and low-flow concentrations and loads were computed using the EGRET Confidence Intervals (EGRETci) R package (Hirsch and others, 2015).