In fens the species composition, vegetation structure and succession rate are determined by vegetation management and water chemistry, particularly by the base status and nutrient status. Base-rich and nutrient-rich surface water causes fens to become eutrophied, which leads to an increased biomass production. When part of fens becomes isolated from this surface water (hydrological isolation), it acidifies due to acidic and oligotrophic rainwater dominance. One consequence of decreasing water quality due to continuing acidification and eutrophication, is the disappearance of the rare plant species that depend on base-rich but oligotrophic water. It is important to obtain quantitative information on the influence of these processes on vegetation structure types and the distribution of rare plant species to support management planning and evaluation. The usual method to obtain this information is fieldwork, but this is time consuming and thus very expensive, especially in large, inaccessible areas like wetlands. The aim of this study was therefore to investigate the efficiency of remote sensing and geographical information systems (GIS) to identify hydrological isolation in order to predict the distribution of rare plant species.De Weerribben study areaDutch inland wetlands are characterized human impacts. The peat cutting and dredging in the 18th and 19th centuries formed a landscape of extensive rectangular bodies of open water (ca. 30 by 1000 m) called petgaten . After the petgaten were abandoned, a process of terrestrialization from open water to fen vegetation began, in which the first stage is the formation of a floating raft of vegetation. The reeds on the floating rafts were mown every year for thatch. When not mown, the open fen becomes a woodland within a few years. During the 20th century most of the fens were drained and reclaimed for agricultural use. De Weerribben (3600 ha), now a nature reserve, is one of the remaining fen areas in the north of The Netherlands (6 o0 'E and 52 o45 'N).Hydrology ...