###### Abstract  
Anthropogenic activities have greatly modified freshwater flows through Everglades National Park (ENP) such that saltwater has intruded extensively inland from the coastline, causing coastal lakes and their ecosystems to be exposed to varying salinity conditions. The Comprehensive Everglades Restoration Plan (CERP) makes an effort to restore the quantity, quality, timing, and distribution of freshwater flow in ENP with a goal of reducing salinity conditions within the coastal communities and adjacent estuaries. An understanding of the temporal and spatial variations of surface water and shallow groundwater salinity in the coastal lakes of ENP is needed to evaluate restoration efforts. Geophysical surveys were conducted between 2016 to 2019 using electrical resistivity and electromagnetic (EM) methods in the coastal lakes of ENP. A mean local formation factor of 10.7 \(\pm\) 1.8 was calculated for the region by comparing the lakes' bottom formation inverted electrical resistivity soundings with coincident pore water resistivity measured in groundwater wells. The conductivity of surface and groundwater increased during the dry season, reflecting decreased precipitation, increased evapotranspiration, and the increasing influence of saline water from Florida Bay. Spatially, salinity in the lakes increased from west to east in the surface water with an opposite trend observed in the shallow groundwater. Along the south to north inland direction, the salinity of both surface water and groundwater decreased. This study demonstrates that floating electrical resistivity and EM methods can characterize the subsurface formation resistivity and describe temporal and spatial patterns of surface and shallow groundwater conductivity. E 2021 2021 13 January 2022 2221 13 January 20222 2221 13 January 20222 2221 13 January 20222 2221 13 January 20222 2221 13 January 202  
the groundwater chemistry in the ENP. Freshwater input to the ENP comes from direct rainfall and inflows from the water conservation area (WCA) reservoirs to the north [4] (Figure 1). The two main flow drainage paths in ENP are the Shark River Slough (SRS) and Taylor Slough (TS) (Figure 1). The two lake regions studied in this project are located between these two main flow pathways. Salinity in Florida Bay varies in time and space and is governed by the influence of precipitation, evapotranspiration, runoff, and mass exchange with the surrounding basins [5]. Evapotranspiration rates are high in this region and affect the freshwater input balance negatively [4]. The author also suggests freshwater inflow is critical to compensate for the net loss. The degree of saltwater intrusion along the coast varies widely and is affected by the hydroclimate variability, hydrogeological setting, history of groundwater development, and sources of saline water within a particular area [6]. Under natural conditions, the seaward flow of freshwater prevents saltwater from encroaching coastal aquifers. However, in comparison with the historical flow of freshwater, the flow of freshwater through the Everglades has been reduced by approximately 70%. Due to this, water quality has degraded, and nearshore dry-season salinities increased by 20 to 30 PSU [7]. This reduced historical flow of freshwater input to the Florida Bay followed by drought in South Florida between 2014 and 2015 produced a substantial die-off of the seagrass [8]. Most commonly, mapping of saltwater intrusion in coastal aquifers has been conducted by collecting water samples from wells. Even though this approach provides reliable results, it is restricted to the existing and accessible wells. Geophysical methods have been developed to identify and map the lateral and vertical distribution of shallow freshwater and saline water interface. These methods provide powerful tools to identify the position of saline or brackish water in an aquifer [9]. Electrical resistivity and electromagnetics are the most commonly used geophysical methods to study saltwater intrusion.