Chitinolytic microorganisms such as bacteria, fungi, and actinomycetes, were isolated from the water and bottom sediments of Lake Chełmżyńskie and the soil of its watershed. The impact of various forms of chitin on the chitinolytic activity of these microorganisms was investigated. Bacteria isolated from the analyzed environments exhibited the highest chitinolytic activity in the presence of colloidal chitin. High activity was also observed in a culture medium containing shrimp shells. The analysis of chitinolytic activity of actinomycetes demonstrated that strains isolated from the soil had considerably higher activity levels than those isolated from lacustrine water and bottom sediments. All soil actinomycetes exhibited the highest activity in a culture medium containing colloidal chitin and shrimp shells. Actinomycetes collected in water and bottom sediments were characterized by similar activity levels. Chitinolytic fungi exhibited the maximum activity also in a medium containing colloidal chitin. The presence of shrimp shells in a culture medium had the lowest impact on chitinolytic activity. Among the analyzed forms of chitin, the impact of chitin powder on the activity of chitinases was the least stimulating.