The Sleepers River Research Watershed, near Danville, Vermont, is a 111-square-kilometer watershed established in 1958 by the Agricultural Research Service.The research watershed has since been operated by three other federal agencies: National Weather Service, U.S. Army Cold Regions Research and Engineering Laboratory (CRREL), and U.S. Geological Survey (USGS). USGS started at the site in collaboration with CRREL in 1991 and has been the sole operating entity since 2000. From 1991 to 2017, the research watershed was part of the national 5-site network of the USGS Water, Energy, and Biogeochemical Budgets (WEBB) program. Since 2017 Sleepers has been funded by USGS Land Change Science to continue the core measurements at the small watershed scale while expanding the geographic scope to the larger Connecticut River basin. This data release brings together the analytical results from more than 15,000 samples into a single spreadsheet ("1. Sleepers River Aqueous Chemistry.csv;" located in file "Sleepers Chemistry Release Files.zip"). Five additional supporting files document different facets of a thorough quality-control effort. One of the challenges posed by this effort was to integrate results from 18 separate laboratories used over the course of the study. The project's operational model encouraged academic collaboration to augment federal funding, and, lacking its own laboratory, frequently relied on student researchers using university laboratories. Harmonizing these various data sources was one objective of this data release effort. Continuity is provided by the U.S. Forest Service laboratory in Durham, New Hampshire, which has analyzed weekly precipitation and stream samples throughout the 30-year project history. The dataset includes major ion chemistry, select metals, and isotopic composition for atmospheric deposition, streamflow, and subsurface waters. The data release is structured as six pairs of data (.csv) and metadata (.xml) files: (1) the main chemistry and isotope dataset, (2) a description of the site names and sampling locations, (3) a description of the 18 individual laboratories used, (4) results of inter-laboratory comparisons, (5) statistics on replicate analyses, and (6) results of blank analyses.