The actinomycetes in water samples and bottom sediments of lowland, eutrophic lake as well as in soil (farmland, sandy) of the lake basin were studied. Chitin-degrading actinomycetes were isolated (with a plate technique) from each habitat; subsequently, their chitinolytic activity (with the fluorometric method) was determined in relation to temperature (10-50[degree]C) and the physical type of chitinous substance (colloidal chitin, chitin powder, and shrimp shells). This study demonstrated that actinomycetes were the most abundant in soil samples (average of 18x10[^3] CFU g[^-1] in farmland soil, 9x10[^3] CFU g[^-1] in sandy soil), and the least abundant in water samples (average of 2.7x10[^1] CFU mL[^-1] in lake water at neutral pH, 0.6x10[^1] CFU mL[^-1] in lake water with alkaline pH). The highest percentage of chitinolytic actinomycetes was observed in soil (average of 80% in sandy soil and 85% in farmland soil). Chitinolytic actinomycetes also made up a large fraction of total actinomycetes in water samples (average of 73%). In silt and sandy sediments, percentages of chitinolytic actinomycetes equaled 23 and 15%, respectively. Actinomycetes collected in soil were characterized by the highest activity (average of 14 nmol MUF mg[^-1] of protein h[^-1] in farmland soil, 8.5 nmol MUF mg[^-1] protein h[^-1] in sandy soil). The lowest activity was observed among benthic actinomycetes (average of 5.4 nmol MUF mg[^-1] of protein h[^-1] in silt, 0.65 nmol MUF mg[^-1] protein h[^-1] in sandy sediments). The impact of temperature and the type of chitinous substrate on the activity of chitinases produced by actinomycetes demonstrated that their activity peaked at 40[degree]C and in the presence of colloidal chitin. Observed differences in actinomycetales number and activity in the lake and the soil may be explained by higher accumulation of chitin substances in the soil. This polymer allows microorganisms to continually synthesize chitinolytic enzymes and take active part in that compound decomposition.
