This study evaluates the biodegradation of carbendazim (1 mg/l) by homogeneous cultures of planktonic (N=25) and benthic (N=25) bacteria as well as by heterogeneous cultures (N=1) containing a mixture of 25 bacterial strains. The bacteria were collected from a 25 cm subsurface water layer and a 5-10 cm surface layer of bottom sediments of lake Chełmżyńskie. Results indicate that bacterioplankton are better able to decompose carbendazim than benthic bacteria (p<0.05). In the case of decomposition by planktonic bacteria, the mean half-life of carbendazim equaled 40 days. Benthic bacteria, on average, required 60 days to reduce the concentration of fungicide by 37%. The level of biodegradation of carbendazim in mixed cultures of benthic and planktonic bacteria after a 20-day incubation period was lower than the average value of its biodegradation in homogeneous cultures. Forty- and 60-day homogeneous cultures of planktonic bacteria were characterized by a higher mean level of carbendazim biodegradation than that of the mixed culture. Decomposition of the fungicide in 40- and 60-day mixed cultures of benthic bacteria was higher than the mean value of biodegradation of this compound in homogeneous cultures. We demonstrated that among planktonic bacteria, the species Sphingomonas paucimobilis, Aeromonas hydrophila, and Pseudomonas fluorescens were the most efficient in reducing the concentration of carbendazim, while among benthic bacteria, Burkholderia cepacia and two unidentified strains of bacillus were the most efficient.