The aim of the study was to evaluate the changes in abundance, species richness, and diversity of epiphytic Gastrotricha in the littoral of a mesotrophic lake. The influence of pH and oxygen on their occurrence was also investigated. Gastrotricha occurred throughout the year: 27 species were identified together, and species richness varied at different seasons. The highest number of species on water vegetation was found in the summer (26 species), while in the winter season only 7 species were present. Species diversity expressed by the Shannon index, in spring, summer, and autumn was high and amounted 2.10, 2.37, and 2.31, respectively. In winter, the value of the index was significantly lower and amounted 0.59. Three species were found to be dominant from spring to autumn with the dominance over 9.0%: Heterolepidoderma macrops Kisielewski, 1981, H. ocellatum (Mečnikow, 1865), and Lepidodermella squamata (Dujardin, 1841). The GLM analysis revealed that number of collected species in spring, summer, and autumn does not depend either on season or on pH and oxygen content. The lowest density of gastrotrichs was found in winter (average of 33 10−3 indiv. m−2), whereas the highest was found in summer (average of 1392 10−3 indiv. m−2). The density differed with season and neither pH nor oxygen content had an effect upon gastrotrich densities.