The Canadian Arctic experiences amplified climate change effects due to extreme temperature sensitivities of the cryosphere. Surface water connectivity, discharge, and runoff are significantly altered under rapid reductions of ice, snow, and permafrost, threatening the spatial and temporal safety and reliability of water, food, and traditional ways of life. The IPCC does not yet fully understand the impacts of permafrost thaw on water balance, which would illustrate regions most vulnerable to change. Stable isotopes in water, oxygen-18, 18O, and deuterium, 2H, provide distinct streamflow source indicators, revealing water storage and flow pathways. To quantify water balance changes and establish a recent-year long-term isotopic framework, an isotope mass balance model for: i) Greiner Lake, and ii) Greiner Lake watershed in Cambridge Bay, Nunavut was constructed from 18O and 2H data on freshwater, snow, and precipitation collected throughout the watershed between 2018-2021. Coupled with a two-component isotope hydrograph separation analysis and water balance calculations, permafrost thaw meltwater can be assumed as the unaccounted late summer streamflow. Climate change scenarios were then stimulated to better understand the implications changing source contributions may have on local water balance on these regions, as well freshwater discharge into the Arctic Ocean, providing a working template to study the changing hydrological regimes of other high latitude watersheds of similar hydrological and geological characteristics.