Groundwater contributions to streams sustain stream discharge over winter and during dry periods, regulate stream temperature and water quality, and buffer river systems against climate variability. As a result, quantifying groundwater–surface water (GW-SW) interactions across spatial scales is essential for effective water management. Hydrograph separation techniques based on geochemical and isotopic streamflow data can be used to estimate groundwater contributions to streamflow from reach to catchment scales. This method requires that groundwater and surface water endmembers are well-characterized and isotopically and geochemically distinct. To support regional assessment of GW–SW interactions, oxygen-18, deuterium analyses were incorporated into select provincial monitoring programs across Alberta. The resulting dataset includes over 1,500 samples from approximately 100 river locations, 70 groundwater wells, 30 snow-core sites, and five monthly precipitation monitoring stations. The new isotope dataset improves spatial coverage for the isotopic composition of precipitation and streamflow across the province and includes monthly time-series data that span the 2024 drought. Preliminary data from these programs will improve understanding of regional controls on isotopic labelling of precipitation and snowmelt and help refine geochemical and isotopic compositions of groundwater endmembers for hydrograph separation studies. Endmember characterization was further evaluated using data from synoptic surface water and groundwater surveys along the Milk River, conducted both prior to and during the 2025 St. Mary diversion failure. Ongoing work will integrate the geochemical and isotopic estimates of groundwater discharge with hydrometric analyses, stream temperature datasets, and modeling approaches to assess groundwater contributions to streamflow generation across the province.