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The aim of this work was to investigate the diversity of diatom assemblages developed in the Przyrwa stream, to assess water quality based on benthic diatoms and to make an attempt at the identification of physicochemical factors having the greatest impact on the differentiation of diatom assemblages. Studies were conducted in 2011-2012 on the Przyrwa stream, a left-side tributary of the Wisłok River flowing through the city of Rzeszów and with its spring section located on the borders of the city. A total of 259 diatom taxa were identified in the Przyrwa stream during three studied seasons. At all investigated sites, the most abundant population consisted of Ulnaria ulna (Nitzsch) Compère, Cocconeis pediculus Ehrenb., Achnanthidium minutissimum (Kütz.) Czarnecki var. minutissimum, Navicula gregaria Donkin, Planothidium frequentissimum (Lange-Bert.) Lange-Bert., P. lanceolatum (Brébisson) Lange-Bert., Navicula lanceolata (C. Agardh) Ehrenb., Amphora pediculus (Kütz.) Grunow, Eolimna minima, (Grunow) Lange-Bert., Melosira varians C. Agardh and Cyclotella meneghiniana Kütz. Based on IPS (Specific Pollution Sensitivity Index) and GDI (Generic Diatom Index) indices, the ecological status of the Przyrwa stream was assessed as moderate to poor (mostly III-IV class of water quality), while the TDI (Trophic Diatom Index) index indicated a poor to bad ecological status (mainly IV-V class of water quality).