As part of a water quality survey, stream samples were collected throughout the Big Creek, Lynn River, and Nanticoke Creek Watershed in Southern Ontario in 2008. The project was undertaken to examine stream water quality under base flow conditions and was done in support of Environment and Climate Change Canada’s ongoing work to assess the status of the waters of the Great Lakes Basin. Sample collection was done at roadside stream crossings using a stainless steel bucket. Field parameters (temperature, specific conductivity, dissolved oxygen, pH) were determined on site using a YSI 600QS Sonde. Water quality parameters (major anions, major cations, select dissolved metals, ammonium) were analyzed at the groundwater labs at the Canada Centre for Inland Waters, Burlington, Ontario. Dissolved organic carbon concentrations were determined at the Environmental Geochemistry Lab, University of Waterloo. Stable isotope ratios of water (δ2H, δ18O) were analyzed at the Environmental Isotope Lab, University of Waterloo.