This data release contains 15 datasets and associated metadata of watershed characteristics and data related to stream water quality and constituent load estimation for 15 study watersheds in Gwinnett County, Georgia. Dataset periods vary but range within 2000 to 2021. The 15 datasets are organized as individual child items. The data release includes three Geographic Information System shapefiles: (1) 01: Watersheds shapefile for the 15 study watersheds in Gwinnett County, Georgia; (2) 02: Stormwater drainage areas shapefile for the 15 study watersheds in Gwinnett County, Georgia, August 2021; and (3) 03: 200-foot stream buffer shapefiles for 15 watersheds in Gwinnett County, Georgia. The data release includes four comma separated value (csv) format datasets related to watershed characteristics: (1) 04: National Land Cover Database land cover at 15 watersheds in Gwinnett County, Georgia from 2001 to 2019; (2) 05: Impervious areas within 15 watersheds in Gwinnett County, Georgia from 2000 to 2020; (3) 06: Property parcel building construction dates and densities in 15 watersheds in Gwinnett County, Georgia in 2021; and (4) 07: Population density in 15 watersheds in Gwinnett County, Georgia from 2000 to 2020. The data release also includes the following eight csv format datasets related to stream water quality and constituent load estimation: (1) 08: Daily average stream base flow at 14 watersheds in Gwinnett County, Georgia for water years 2002-2020; (2) 09: Streamwater quality assurance sample results for 19 water-quality constituents in 15 watersheds in Gwinnett County, Georgia for years 2000-2020; (3) 10: Laboratory standard reference samples for the Gwinnett County, Georgia study for years 2014-2020; (4) 11: Streamwater sample constituent concentration outliers from 15 watersheds in Gwinnett County, Georgia for water years 2003-2020; (5) 12: Model calibration data for fitting regression models used to estimate streamwater loads for 12 constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020; (6) 13: Models coefficients and statistics for regression models used to estimate streamwater loads for 12 water-quality constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020 (includes 488 portable document format files (pdf) with reports and plots for evaluating model fits); (7) 14: LOADEST estimation dataset used to estimate streamwater loads for 12 constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020; and (8) 15: Streamwater load and yield estimates for 12 constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020.