During the years 2004-2006 the parasitological autopsies of three species of fish: roach Rutilus rutilus (L.), bream Abramis brama (L.) and perch Perca fluviatilis L. from three lakes situated in warmińsko-mazurskie voivodeship were done. The aim of this study was comparable analysis of Metazoan parasite communities which occur in roach, bream and perch in three lakes of river Łyna watershed. These lakes differ by physical (size, depth, eutrophication degree) and biological factors (composition of free-living organisms). The studies showed some relationships between size of fishes and the frequency of some parasite species as well as some relationships in seasonal dynamic of occurrence and maturation of ecto- and endoparasites, which were connected with temperature--main factor regulating processes of fish colonization by parasites and future development of parasites. In quantitative and qualitative analysis of fish parasite community structure the following indexes were used: species richness (S), species diversity of Shannon-Weaver (H'), species diversity of Brillouin (HB) and index of domination Berger-Parker (D). Studies showed that the main indexes of communities structure which indicating on occurring differences between lakes were indexes of diversity component communities and infracommunities and also index of dominance. Communities of monogeneans (roaches and breams) can be use as indicators of water environment. Apart from communities of gills parasites also alfamesotrophic lake Łańskie and eutrophic Mielno lake were differenced by eyes parasites and allogenic community of bream parasites and by intestinal parasites of roach.