The authors investigated the mycoflora developing on the dead specimens of Pallasea quadrispinosa from Lake Hańcza. Water for experiments was collected from four different bodies of water: Hańcza Lake, Wigry Lake, Supraśl River and Fosa Pond. A total of 41 zoosporic fungus species were found to grow on the dead of Pallasea quadrispinosa specimens, including 17 species inducing mycosis in a number of freshwater specimens, including 17 species inducing mycosis in a number of freshwater fish species: Achlya debaryana, A. diffusa, A. dubia, A. klebsiana, A. orion, A. polyandra, A. prolifera, A. proliferoides, Aphanomyces laevis, Dictyuchus monosporus, Leptolegnia caudata, Saprolegnia delica, S. ferax, S. hypogyna, S monoica, S. parasitica and and Thraustotheca clavata. Aphanomyces astaci as a parasite of noble as a parasite of noble crayfish, causing the so called crayfish plague, was also observed on Pallasea quadrispinosa.