A study on the occurrence and chitinolytic activity of planktonic, benthic and epiphytic bacteria was carried out in the Moty Bay of lake Jeziorak near Ilawa. The greatest number of chitinolytic bacteria occurred on macrophytes. In terms of percentage, the chitinolytic bacteria share among heterotrophic bacteria was much greater in epiphytic and planktonic bacteria than in benthic ones. When confronted with colloidal chitin all the investigated strains showed maximum chitinolytic activity after 96 h incubation and the minimum one after 48 hours. The greatest total chitinase activity was recorded in planktonic bacteria, while specific activity - in epiphytic bacteria.