The aim of this study was to evaluate Gambusia spp. (mosquito-fish) mercury bio-concentration factor in relation to marsh surface water sulfate concentration. As part of the everglades regional environmental monitoring and assessment marsh biogeochemical parameters were collected by the US Environmental Protection agency between 1995 and 2005 within the Everglades Protection Area and Everglades National Park (ENP). Surface water sulfate and methyl-mercury concentration data in combination with mosquito-fish total mercury concentration data was used to elucidate the gambusia mercury bio-concentration and surface water sulfate relationship. Previous studies hypothesized that the relationship of biota mercury and surface water sulfate concentrations is unimodal. However this study shows that the relationship of biota mercury and sulfate surface water concentrations in mosquito-fish adheres closely with a log-log relationship. Furthermore mosquito-fish bio-concentration factor were similar for Water Conservation Area (WCA) 1 and WCA2, while WCA3 and ENP were significantly different between all pairs throughout the study period. This difference in hypothesized relationships versus the relationship defined in this study could be the result of life span (extent of exposure) or life history of mosquito-fish.