This data release contains information to support water quality modeling in the Delaware River Basin (DRB). These data support both process-based and machine learning approaches to water quality modeling, including the prediction of stream temperature. This section contains observations related to the amount and quality of water in the Delaware River Basin. Data from a subset of reservoirs in the basin include observed daily depth-resolved water temperature, water levels, diversions, and releases. Data from streams in the basin include daily flow and temperature observations. Observations were compiled from a variety of sources, including the National Water Inventory System, Water Quality Portal, EcoSHEDS stream water temperature database, and the New York Department of Environmental Protection. The data are formatted as a single csv (comma separated values) or zipped csv. Site observation data were matched to stream reach segments, and the data files included contain identifiers for both observation sites and affiliated stream reaches. Please see metadata for <a href="https://www.sciencebase.gov/catalog/item/623e54c4d34e915b67d83580"> 1) Spatial data for rivers, reservoirs, and monitoring locations </a> for further information on how monitoring location sites were matched to river segments. For modeling purposes, we created a holdout test set of flow and temperature observations that were representative of dynamics throughout the Delaware River basin from water year 1980-present. Test holdouts are documented in the flow and temperature files, and details describing the holdout decisions can be found in Oliver et al. (2021).