In the present work 35 150 water beetles of 6 families and 244 species were screened. Water mite larvae of the genus Eylais were found on 76 species of beetles of the families Haliplidae, Dysticidae, Gyrinidae, Hydraenidae, and Hydrophilidae. Twelve Eylais species were found, the most of them being E. longipalpis, E. extendens, R. relicta (?), E. setosa, E. muelleri, E. undulosa,and E. sp. The infestation rate was generally low, reaching at maximum 11.9 % of the specimens of species. E. hamata, E. bisinuosa, and E. glubokensis were found on a single beetle species. The other species are parasites on more than one species, but showed preferences. Larvae were located under the elytra. The size of the larvae varied from 0.13 to 7 mm. The relations between the body size and the data of sampling suggest a prolongation of the reproduction nearly over the entire spring-summer period, or the occurence of more than one generation during the year. The environmental diversity of parasitism indicates a partial separateness of the infection and parasitism zones, probably due to the extensive mobility of the host.