Groundwater is used for drinking water in many rural coastal communities that often lack the adaptive capacity and resources to protect their vulnerable water resources. Along the coast, a wedge of saline groundwater is separated by overlying fresh groundwater through a salinity transition zone that is maintained by water density differences and is in a delicate equilibrium with atmospheric and oceanic forcing on the aquifer. Accordingly, the transition zone thickness and location are influenced by many factors including sea-level rise, recharge, and precipitation changes. Landward movement of this transition zone is known as saltwater intrusion, a process that threatens coastal groundwater resources. The overall goal of this study is to investigate saltwater intrusion in Prince Edward Island, Canada’s only province that relies entirely on groundwater for drinking water. Field and modeling efforts are focused in PEI National Park and the adjacent peninsula community (Stanhope) that has experienced elevated salinity levels in wells. Coastal groundwater observatories, embayment monitoring, and locations for repeated geophysical surveys were established around the peninsula to investigate groundwater dynamics and ocean-bay-aquifer mixing. A numerical model has also been developed in MODFLOW6 to explore the impacts of future climate conditions and anthropogenic activities, including rising sea levels, changes in groundwater recharge, and increased groundwater pumping. The geophysical surveys, groundwater monitoring and numerical modeling suggest a complex transition zone around the peninsula. Findings from this study will help inform coastal protection guidelines for rural communities in PEI and similar coastal jurisdictions worldwide.