The composition of diatom assemblages of epilithon, epiphython and epipelon in the Shchu­gor River was presented. Biofoulings of rocky substrates, macrophytes, filamentous algae and samples from the surface of bottom sediments were studied. The diatom assemblages had a diverse composition and included 218 species with varieties and forms from 60 genera, 27 families and 12 orders. The order Naviculales (56 taxa) and the family Fragilariaceae (39 taxa) played a major role. The genera Gomphonema (17 taxa), Nitzschia (16), Navicula (14), Eunotia (14) were dominant by the species abundance. The identified diatoms were mostly epiphytes, indifferent to salinity and alkaliphilous species, clean water indicators. The most common community in the river was epilithon, whereas epiphyton distinguished by the most diverse composition. The epipelon was poorly developed, having the lowest number of diatom taxa.

Dominant, subdominant, accompanying species of the diatoms were very similar in different phytobenthos groups, the Sørensen-Czekanowski coefficients varied from 0.70 to 0.81. The dominant species were Achnanthidium minutissimum, Encyonema minutum, Fragilaria gracilis, Gomphonema exilissimum, G. ventricosum, Hannaea arcus, Meridion circulare. The sub-dominant species were Cocconeis placentula, Nitzschia fonticola, Ulnaria ulna and Staurosirella pinnata. Based on the Berger-Parker and Simpson variety indices, the occurrence of taxa in the genera and families in the epiphyton was more uniform. The assessment of benthic diatoms demonstrated that the Shchu­gor River is a typical mid-mountain river. Diatom communities of epilithon, epiphython and epipelon can be used for the monitoring of ecological status of the river.