The authors investigated zoosporic fungi developing on 17 species of leeches (Hirudinea) in six bodies of water of various trophic states. A total of 101 zoosporic fungus species were noted, with predominance by the Saprolegniales (65) and Peronosporales (21). Of 101 fungus species found, 38 have been fish para-sites or necrotrophs. Four fungus species were recorded for the first time in Polish waters.