Freshwater bryozoans belong to a group of colonial invertebrates. Bryozoa in Czech translation means moss and animal. Representatives of bryozoans, are at first glance very similar to moss and plants from other species differ considerably. The main objective of this thesis is to determine the different species found in the territories Koterov and Old Plzenec, to check the ecological demands of species found, to evaluate the seasonal dynamics of occurrence bryozoans and to compare the data with the available literature sources. The monitored stretch of the river Úslava has been divided into 10 sites. Five locations were explored on the Koterov territory and on the territory of Old Plzenec another 5 locations aswell. At both locations, a total of 150 samples of these bryozoans have been collected and determined 233 zoarias. Total number of 5 species of freshwater bryozoans were founded in the observed area Koterov - Starý Plzenec: Plumatella emarginata (Allman, 1844), Plumatella fungosa (Pallas, 1768), Plumatella repens (Linné, 1758), Fredericella sultana (Blumenbach, 1779) a Paludicella articulata (Ehrenberg, 1831). Individual species were determined by a synoptical key from athors Wood and Okamura (2005) From the obtained results, there has been evaluated a seasonal dynamics of the representation of individual species during July, August and September. In addition to the seasonal dynamics, light requirements and preferences of the species and the occurences of particular species were evaluated. In the Koterov area, Plumatella emarginata has occured most widely, second common type was Plumatella fungosa. There were less abundant species of Fredericella sultana and Paludicella articulata. A type Plumatella repens was found only rarely. on the teritorry of Old Plzenec, most frequently Plumatella fungosa did appear, secondly, Plumatella emarginata. The least recorded species were Plumatella repens and Fredericella sultana. Most frequently, all the species were occiring on the top and sides of the stones. Plumatela fungosa, Plumatella emarginata and Paludicella articulata were mostly recorded on the upper and lateral sides of the stones. Types Fredericella sultana and Plumatella repens were plentiful on the upper sides of the stones. The reason for this occurrence on the upper side could be a rich food supply. On the flank, the species are probably well protected from predators. The undersides of the stones were inhabitated rarely, probably due to insufficient supply of the oxygen. My observation of Paludicella articulata being one of the shade-liking species are in line with the findings from the availiable literature . The other species were found both at shaded and sunlit sites and it cannot be percisely determined, if teh lighting conditions have major role in their development.