Studies on the occurrence of aquatic fungi in the bathing sites of the river Supraśl in Podlasie Province of northeastern Poland were conducted in the years 2001-2003. Some hydrochemical analyses were performed using standard methods. Bait method was used to isolate the fungi. The following species were identified: fish pathogenic fungi – Achlya orion, Aphanomyces laevis, Dictyuchus monosporus, Saprolegnia ferax, S. monoica, and S. parasitica; human pathogenic fungi – Aspergillus candidus, Candida albicans, Lagenidium humanum, Penicillium mycetomagenum, Rhizophydium keratinophilum, and Trichosporon cutaneum; and phytopathogenic fungi – Achlya racemosa, Pythium butleri, P. myriotylum, and P. debaryanum. Physicochemical parameters of water in the bathing sites had no important effect on the presence of fungi.