The snail fauna of human-transformed forests (originally ranging from oak-hornbeam to alder swamps) at Lake Hańcza and two nearby lakes in NE. Poland includes 29 species, with 14–18 species per site. There are also four slug species. The ten sampling sites vary rather much in their species composition, the mean Nei index being 0.71 and IMAX 1.57; the heterogeneity does not seem to result from sampling error. In most sites 1–3 species contribute over 50% of total abundance. Most species recorded are common, euryoecious and widely distributed; restricted forest snails, timber-dwellers and vegetation climbers are nearly absent.