A comprehensive study to evaluate water-quality trends in the International Souris River Basin, Saskatchewan and Manitoba, Canada and North Dakota, United States was completed by the U.S. Geological Survey (USGS) in cooperation with the International Joint Commission and International Souris River Board. This page contains water-quality data for stream and reservoir sites in the Souris River Basin in North Dakota, Saskatchewan, and Manitoba. Each file contains information on major ions (MI), nutrients (NUT), trace metals (TM), sediment (SED), and dissolved oxygen (PHY). These data contain numerous columns that are described in the entity and attributes of these files. These files contain the water-quality observations for the statistical summary tables in the report cited in this data release (Nustad and Tatge, 2023).The siteinfo.table.csv file can be used to cross reference the sites with the main report (Nustad and Tatge, 2023).