The authors investigated the influence of the iron bacteria Sphaerotilus natans on occurrence of aquatic fungus species in the water of four water bodies of different trophy. The seeds and snake exuviae were used as baits. The fewest fungi were noted in the containers with bacteria and control in water from Pond Akcent (most trophy), the most in containers in water from Pond Dojlidy (fewest trophy). More fungi were found to grow in the control containers (Co) than in the containers with bacteria (Bc) in water from all water body. The mean ratio of Co/Bc ranged from 1.8 (Pond Dojlidy) to 3.3 (Pond Akcent).