The discharge of nutrient and ion-enriched agricultural and urban runoff into perimeter canals surrounding the Arthur R. Marshall Loxahatchee National Wildlife Refuge and subsequent intrusion into a natural soft-water marsh is causing ecosystem alterations. Because this habitat is among the last remaining rainfall-driven areas of the Florida Everglades, understanding the dynamics of canal water intrusion is important for marsh protection and restoration. Using conductivity sondes, we examined canal water movement in and out of the marsh along four transects based on 350 and 500 µS cm⁻¹ conductivity isopleths. Canal water intruded into the marsh to different extents, with the greatest intrusion observed on the west side of the refuge. Canal water was always evident in the marsh, and the maximum measured intrusion was 3.9 km from November 2004 through January 2006. Stage differences between the canal and marsh influenced the movement of water into and out of the marsh, with high inflow rates in the canal increasing intrusion into the marsh. Marsh areas with sediment elevations < 4.9 m were most sensitive to canal water movement. Our analyses will contribute to the understanding of hydrologic conditions that lead to pollutant intrusion into floodplain wetlands.