This paper concerns part of a monitoring study and contains the results of 20-year observations on the species diversity and dynamics of the count Candida genus fungi which inhabit surface waters. The research material consisted of water samples collected from the Łyna River, the main river of the Warmińsko-Mazurskie Voivodeship, within the administrative boundaries of the city of Olsztyn. The samples were subjected to routine diagnostic testing applied in hydromycological studies. The obtained fungi isolates were determined, documented photographically and deposited in a strain collection of the Department of Microbiology and Mycology at the University of Warmia and Mazury in Olsztyn. A total of 23s of the Candida genus were isolated, including six species in the teleomorphic stage. It was noted that over the past decade, the taxonomic diversity of the fungi had increased significantly (from 2 to 23 species). Potential anthropopathogens had also emerged. Over the twenty-year period of observations, the species that were always isolated were Candida albicans and C. guilliermondii, characterised by high pathogenicity and bioindicative properties, which are important in the epidemiology of fungal infections.