Endopsammic algal communities from shallow littoral sediments in a subeutrophic Lobelia lake are presented. The flora in the studied lake consisted of 492 taxa. During the two years of study, the density of algae fluctuated between 0.65x103 and 23.24x103 individuals in 1 cm3 of sand and resulted mainly from growth of cyanobacteria, green algae and diatoms. The poorest communities occurred in spring, the most abundant in summer and autumn. In 1985, cyanophytes dominated (up to 92%) and Aphanotece microscopica in particular; the latter species grew in masses, particularly in summer and constituted more than 50% to 64% of the total quantity. In the next year, greater abundance of green algae, diatoms and desmids was noted, probably owing to the higher concentration of nutrients in interstitial water. The most suitable conditions for algal growth created sediments of flat bottom stabilized by isoetids. Mass development of certain cyanobacteria species resulted from medium trophy of the lake.