Genetic variability of two populations of Arctic freshwater crustacean Lepidurus arcticus (Crustacea, Notostraca) occuring in small tundra reservoirs near the Polish Polar Sta− tion in Hornsund (Spitsbergen) was studied. The allozyme polimorphism analysis of 11 en− zyme systems indicates a considerable distinctness and genetically heterogeneous character of the populations of L. arcticus inhabiting freshwater reservoirs of similar hydrological con− ditions situated close to each other (2 km). Our research revealed a complicated and geneti− cally heterogeneous character of the populations. Three hypotheses about genetic structure and type of reproduction were tested: hypothesis M – the free transfer without assigning a clone for particular reservoir and the lack of doublemutations; hypothesis I – separation of in− dividuals between reservoirs and the possibility of doublemutations; hypothesis S – presence of partial sexual reproduction in the population, probably with males. In conclusion participa− tion ofmales in reproduction is probable, despite their presence was not recorded in our study. Males usually occur in low numbers or not every year. The populations' clonal structure as well as the genetic diversity typical of species reproducing sexually was observed. The Hardy−Weinberg genetic equilibrium is maintained as new clonal lines appear due to the ge− netic diversity increasing incidentally as a result of sexual reproduction.