Minimally disturbed lakes were determined from available GIS data (e.g. land use, roads, aerial photography) for comparative use in EPA’s national survey of lake health. A series of maps was generated for each candidate reference lake and analyzed for evidence of disturbance. Digital land cover and roads data were used to characterize disturbance throughout each lake watershed. Lakes which passed this screening were further examined for evidence of disturbance within a 100 m buffer around the lake shoreline. A set of reference lakes was selected for sampling and used for comparative analysis in EPA’s 2007 National Lake Survey reporting of randomly selected lakes.