Groundwater flow in discontinuous permafrost is complex and often unpredictable. Frozen-soil obstructs flow causing groundwater to re-route through thawed zones comprised of hydraulicly conductive soils. Open taliks connect sub and suprapermafrost portions of aquifers creating mixing of groundwater from these two zones with different water qualities. In this study, spatial and temporal distributions of stable isotopes 2H and 18O measured in a floodplain aquifer were used to characterize groundwater flow in a discontinuous permafrost aquifer located in a river floodplain. Results show enrichment in 2H and 18O in shallow suprapermafrost groundwater through mixing of more enriched precipitation recharge water with more depleted river recharge water. Conversely, subpermafrost groundwater is depleted in 2H and 18O, similar to δ18O and δ2H concentrations in river water. Low concentrations of δ18O and δ2H measured at the water table identify areas of upward flowing subpermafrost groundwater through open taliks into the suprapermafrost portion of the aquifer. These open taliks are located along slough channels and randomly located throughout the large body of permafrost positioned in the floodplain. Well logs and the detectable decrease in δ18O and δ2H in areas where open talik exist show that the soils in open taliks are comprised of highly hydraulic conductive sands and gravels compared to frozen soils which are mainly silt. Results from this study show the process of permafrost degradation in floodplain aquifers consisting of rapid thawing in areas of highly permeable soil versus slow conductive heat transfer into low permeable silt layers.