Ecological changes in plant communities in several Florida lakes have been noted by biologists in the past, but rarely have the parameters of these communities been documented for future reference. Soil moisture is an important factor in determining which plants will occur at particular elevations, but more important is the inundation tolerance of the various species. The purpose of this study was to compare the long range effects of water level fluctuation on the marsh vegetation of Lake Okeechobee. The Florida Game and Fresh Water Fish Commission, in 1956, conducted a vegetational analysis of the lake marsh in order to predict the probable results on vegetation from construction of a levee to contain the lake waters. A subsequent analysis of the same area was conducted by Commission personnel in 1969 to determine what vegetational changes had occurred. Comparison of the data from the two studies revealed that stabilization of the water level had occurred resulting in perennials replacing annual plants, an increased frequency of submergent species, and a decrease in total number of species present.