Summary Subject of this lasting study started in 1989 is an inner mesotrophic lake of Valamo Island (North-Western Russia) - Leshevoe Lake, with maximal depth 14m, and usual 2-3m. Overall length of the lake is about 3000m. During the period of study (1989-2000) a total of 250 repetitive and single samples were collected and treated in all seasons. A total of 32 species of Gymnamoebia were found (about 20% of total known species). 14 of them are new for science. An original method of amoebae enumeration, elaborated in course of this work, allowed to estimate their abundance in the sediments, in respect to their vertical distribution. Number of amoebae was varied from 9.2 to 69.7 mln ind/m-2, which is comparable with that of ciliates in similar habitats. Three ecological groups of species, according to the typical patterns of their vertical distribution, were established. This must be taken into account in further ecological and faunistical studies. Irregular species distribution and sufficient fluctuations of amoebae species composition during different seasons and years may be explained by mean of the hypotesis of "hidden communities".