-Physical and chemical characteristics of habitats and species diversity in streams and rivers are strongly infl uenced by the catchment area. We analysed the infl uence of selected environmental and spatial variables on the diversity and species composition of epilithic diatom communities in periphyton. Samples were collected along the river course in a torrential river the Kamniška Bistrica. Sampling sites were selected in reaches distributed from the source to the outlet of the river and were under different infl uences from the catchment area and with different physical and chemical characteristics. The most common and dominant diatom species in the periphyton community were Achnanthes biasolettiana and A. minutissima. Achnanthes species often inhabit rivers and springs with moderate organic pollution. Another common diatom taxon was Gomphonema pumilum -a key species indicating oligosaprobic conditions. The results of the canonical correspondence analyses revealed that variance of the periphytic diatom community was explained by water temperature and conductivity as well as altitude. Diatom species richness was positively correlated with saprobic index values and abundance of fi lamentous algae in the river bed indicating a relatively low organic matter and nutrient input into the river system.