Nutrient and ion-enriched agricultural and urban runoff discharged to canals surrounding the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge), threaten historically soft-water ecosystem health.  Canal waters intrude into the Refuge’s interior marsh and cause ecosystem alterations such as converting sawgrass to cattail.  To protect the Refuge ecosystem, understanding canal water intrusion is an important goal.  Daily values from thirty-two conductivity sondes deployed in the Refuge were used to further our understanding of intrusion.  We examined canal water movement in and out of the marsh along four transects as a function of distance based on two conductivity isopleths of ecological relevance and described the driving forces associated with canal water intrusion in the marsh.  Results indicate canal water was always present in the marsh with the greatest intrusion observed on the west side of the Refuge and in areas with sediment elevation below 4.45 m msl.  Canal-marsh stage difference influenced the movement of water in and out of the marsh and high inflow rates to the canal extended intrusion into the marsh.