Sleeping Bear Dunes National Lakeshore was established in 1970. When land acquisitions are completed, the new parkland will consist of portions of the coastal mainland in northwestern lower Michigan and North and South Manitou Islands in Lake Michigan. Since this is one of the more recently acquired natural areas in the National Park Service system, background environmental information was needed to provide a sound foundation for future management decisions. Terrestrial features and cultural history of this region has been documented (e.g., Hatt, 1948, Rogers, 1966; Vent, 1973) but information on inland aquatic resources was lacking. The University of Michigan Biological Station, at the request of the National Park Service, conducted investigations to provide a baseline of environmental data on the Lakeshore’s inland water bodies. A previous report (Stockwell and Gannon, 1975) contains results of water quality studies on the lower Platte River system and its associated lakes within the mainland boundaries of the National Lakeshore. This report provides a limnological survey of Florence Lake, the only inland lake on South Manitou Island. This data can be used for comparison with subsequent monitoring studies to detect changes in environmental quality and determine the extent to which the lake and its watershed can support recreational activity without sacrificing quality.