We investigated the stable isotope hydrology of Sable Island, NS, Canada over a four year period from September, 2017 until August, 2021. The δ2H and δ18O values of integrated monthly precipitation were weakly seasonal and ranged from -66 to -17 per mil and from -9.7 to -3.1 per mil, respectively. Fitting these monthly precipitation data resulted in a Local Meteoric Water Line (LMWL) defined by: δ2H = 7.28±0.22×δ18O + 7.95±1.38 per mil. Amount weighted annual precipitation had δ2H and δ18O values of -37±12 per mil and -6.1±1.6 per mil, respectively. Deep groundwater had more negative δ2H and δ18O values than mean annual precipitation, suggesting recharge occurs mainly in the winter, while shallow groundwater had δ2H and δ18O values more consistent with mean annual precipitation or mixing of freshwater with local seawater. Surface waters had more positive values and showed evidence of isolation from the groundwater system. The stable isotopic compositions of plant (leaf) water, on the other hand, indicate plants use groundwater as their source. Fog had δ2H and δ18O values that were significantly more positive than those of local precipitation, yet had similar17O-excess values. Our results establish an important framework for ongoing isotopic studies of feral horses and other wildlife on Sable Island. Reference:Koehler, G., Hobson, K., 2022. The Stable Isotope Hydrology of Sable Island, NS, Canada. https://doi.org/10.1002/essoar.10510418.1