During studies concerning the occurrence of some fungi and fungus-like organisms in the Biała River in Bialystok, forty-three species were established. Among 34 straminipilous fungi, the most common species were Achlya americana, A. debaryana, A. polyandra, Aphanomyces laevis, Dictyuchus monosporus, Pythium debaryanum, Saprolegnia ferax, and S. parasitica. New for the Polish fungal biota were Achlya ambisexualis, Calyptralegnia basraensis, and Achlya papillosa. Achlya crenulata, A. diffusa, A. flagellata, Aphanomyces stellatus, and Pythium afertile were considered rare. Physical and chemical analysis showed that the water of Biała River in Białystok had a high content of ammonium nitrogen and phosphate, reflecting poor cleanliness.