Aquatic fungi and fungus-like organisms, growing on nuts of seven birch species (Betula gracilis, B. humilis, B. lutea, B. nana, B. papyrifera, B. pubescens and B. verrucosa) found in the water of three limnologically and trophically different water bodies (spring, river and pond), were investigated. The total of 63 species, including 23 fungus-like organisms and 40 fungal species were found on the nuts of the investigated birches. The most common species were Karlingia rosea, Nowakowskiella macrospora, Achlya americana, Aphanomyces laevis, Saprolegnia ferax, Acrodictys bambusicola, Angulospora aquatica, Arbusculina fragmentans, Canalisporium caribense, Heliscus lugdunensis, Pithomyces obscuriseptatus, Tetracladium marchalianum and Tripospermum camelopardus ). Most of the species were observed on the nuts of Betula verrucosa (49 species) and the fewest on the nuts of Betula nana (42). In Cypisek spring, the number of fungal species and fungus-like organisms on the nuts was closely associated with the concentration of chlorides.However, in Supraśl River and Dojlidy pond it was associated with the sulphates concentration (in both cases negative correlation).