<p>Freshwater bodies perform a very important role in the ecological network and they are of great importance for biodiversity conservation. Because of their quick response to local and regional changes in environmental conditions, they are sensitive indicators of ongoing processes. Many users of these freshwater bodies need (or need to develop) a certain ecological quality. To optimize the ecological function of lentic freshwater systems a good understanding of their condition and occurring changes is needed and a specific reference situation is required. A classification that leans on a broad ecological base is essential. To have, in the future, a more objective and effective way to perform nature conservation, to prioritize nature development ect, we need to map the different types of freshwater bodies. We also need more knowledge related to environmental circumstances who can secure sustainable development of aquatic communities. The main objective of this study include the simplification of the main variety of permanent lentic freshwater systems in Flanders into workable units for environmental assessment, management and planning. A hierarchic typology will be worked out, based on biotic and ecological characteristics of key factors. The data collected in this context they are also important for determining the ongoing ecological status of still waters and to develop specific targets and a pragmatic evaluation method.</p>