The authors investigated the influence of the sponge Eunapius fragilis occurred on dead reed Phragmites australis (reed-sponge) on occurrence of aquatic fungi species in the water of five water bodies of different trophic levels of trophism. Seeds and snake exuviae were used as baits. The fewest fungi were noted in the containers with reed-sponge and control in water from Pond Fosa (most trophic), the most with containers in water from Lake Blizno (fewest trophic). More fungi were found to grow in the containers with reed-sponge (Rs) than in the controls (Co) in water from all water bodies. The mean ratio of Rs/Co ranged from 2.3 (Lake Blizno) to 4.5 (Pond Fosa). The effect of reed-sponge on the abundance of aquatic fungi species is probably caused by dissolved organic matter produced during photosynthesis by Zoochlorella sp., a symbiont of the sponge, and excreted into the environment. This excreted organic substance serve as a nutrient for aquatic fungi. Aphanomyces volgensis was recorded in Poland for the first time.