ABSTRACT: The coastal dune lakes of northwest Florida are globally rare ecosystems with intermittent connections to the Gulf of Mexico that result in mix of freshwater and estuarine characteristics. They are managed as freshwater lakes, but most lakes are not protected by numeric nutrient criteria. This study examined 13 coastal dune lakes in Walton County, Florida, through multivariate analyses of water quality data using principal component analysis, cluster analysis, and hypothesis testing with a similarity profile. A classification analysis revealed three lake classes: fresh, mixed, and estuarine. A temporal analysis revealed that the lakes did not change class over ten years, with the two exceptions likely the result of physical changes to the Gulf outlets of those lakes. Climatic variation was evident in all lakes, which affected outlet connection type and frequency, and suggested that phytoplankton biomass accumulation was limited by water residence time. Lake morphology, geographic orientation, and density stratification appeared to cause frequent bottom hypoxia in two of the lakes. A comparative analysis showed that the coastal dune lakes are more similar to the regional estuary, Choctawhatchee Bay, than to a regional freshwater lake. Existing water quality data were used to develop proposed numeric nutrient criteria.