The Biała Tarnowska River is a right-bank tributary of Dunajec. It flows from the Low Beskid Mountains, flowing on the border of Ciężkowickie and Rożnowskie foothills and then flows into the Dunajec on the territory of Vistula Lowland (Nizina Nadwiślańska). The aim of this work was to investigate the diatoms diversity at the individual sites and attempt to evaluate pollution of the river with the use diatoms as water quality indicators. The waters of Biała Tarnowska River were characterized by alkaline or circumneutral pH. Values of nitrates concentration indicated II water quality class, only at the last site (5) corresponded to the standards for the I class. At the studied sites located along river course 205 diatom taxa were identified. The riches in species were genera: Nitzschia (29), Navicula (21) and Gomphonema (15). The most popular dominant was Achnanthidium pyrenaicum (Hust.) Kobayasi. Very numerous communities were created by Navicula lanceolata (Agardh) Kütz, at the lower current of river, on two last sites. In order to determine the ecological status of Biała Tarnowska River the analysis of the diatom assemblages structure was performed. The results of the analysis were shown by the selected diatomaceous indices. According to IPS index Biała Tarnowska has a good ecological status (II class) at the most of study sites. Values of TDI index were the worst and indicated poor and bad water quality (IV and V class) especially in middle and lower current.