We analyzed the species composition of fungi and straminipilous organisms in relation to hydrochemical conditions in six lakes within the Elckie Lake District. The mycological investigations conducted in two vegetative seasons (2014-15) identified 44 species (eight aquatic fungi and 36 straminipilous organisms). The largest number of fungus species were found in lakes Lasmiady (23), Szarek (22), and Krzywe (20), and the fewest were detected in Elckie (12), Rajgrodzkie (13), and Drestwo (14). The diversity of the quantitative and qualitative composition of the mycobiota was probably associated with the content of biogenic compounds and organic substances in the water. The elevated levels of these parameters (lakes: Lasmiady, Szarek, and Krzywe) stimulated the growth and development of fungi and straminipilous organisms, whereas very high levels of biogenic compounds and organic matter (Lake Elckie) and their very low content (Lake Drqstwo) had an inhibitory effect. Among the isolated taxa, there were parasites of amphibians and their spawn, and fish and eggs, including Achlya americana, Ac. polyandra, Saprolegnia parasitica, and S. ferax. Some species included pathogens of crayfish and other aquatic crustaceans such as Myzocytium microsporum, M zoophthorum, Aphanomyces astaci, and Ap. daphniae. Some fungi appeared to be potentially pathogenic to humans, like Aspergillus niger and Candida tropicalis. Such species as Achlya klebsiana, Ac. prolifera, Leptolegnia caudata, Nowakowskiella elegans, N. macrospora, Pythium inflatum, and Saprolegnia litoralis were common phytosaprobionts. Statistical analysis of the results was conducted to determine a correlation in the number of the species of fungi and straminipilous organisms with such hydrochemical parameters as the levels of oxygen, carbon dioxide, and biochemical oxygen demand within a five-day period (BOD5) chemical oxygen demand (COD), calcium carbohydrate, nitrate nitrogen, phosphates, chlorides, dry mass, dissolved substances, and suspension. The differences noted in the species composition of the mycobiota in the lakes studied resulted from, among other things, the physicochemical properties of water. Such parameters as the contents of oxygen, nitrate nitrogen, phosphates, dry residue, dissolved substances, and suspension showed a positive correlation, whereas carbon dioxide, BOD5, COD, calcium carbohydrate, and chlorides correlated negatively with the number of the isolated taxa.
