The main goal of our research is to verify the existence of a model of succession in lake fauna based on the example of water beetles. To contribute to this aim, we have completed a study on 28 harmonic lakes in northern Poland. Water beetles were captured from six different littoral mesohabitats: sandy bottom, Lobelia sp., rushes and bulrushes, non-sandy bottom, Phragmites sp., and sedge stands of the shallowest littoral zone. The relationship between the number of species and the degree of succession is not linear. In the final stages of succession, species richness becomes impoverished. On the other hand, lake succession has a clear influence on changes in the ecological structure of fauna, i.e. the mutual quantitative relationships between ecological groups. The beetle fauna in the transitional stage of evolution (mesotrophic lakes) is most typical of lakes. With consecutive stages of the succession of harmonic lakes, a decrease in the share of the lake component was observed, while the share of generalists increased. These changes are directional and indicate clearly some degradation of lake fauna as a result of the lake’s evolution. Their causes should be sought on different spatial scales – at the lake’s catchment level (type of land use), immediate surroundings, the shoreline (height of the shores, degree of macrophyte development, type of substrate) and water parameters, mainly oxygen saturation and electrolytic conductivity. Some of these conditions, for example, the nearest surroundings of a lake (share of natural and semi-natural land relative to the anthropogenically transformed land, or the height of lake shores) may additionally cause certain modifications in the succession of lakes. Irrespective of the stage of succession, the lakes surveyed provide favourable conditions for many species that are rare and endangered throughout Europe.