Spatial dynamics, abundance and the biodegradation potential of aquatic microbial communities were studied during the period from November 1993 until September 1995 in the Kohtla-Jarve region of north-eastern Estonia. General trends in bacterial population density profiles indicated that the microbial community and the heterotrophic, lipolytic, denitrifying bacteria and biodegradative bacteria (phenol, m-toluate, benzoate, salicylate, camphor, naphthalene and heptane degrading bacteria) were strongly inhibited in the highly polluted wafers with ail shale ash leachate effluent and the bacterial numbers increased as the pollution load decreased. Microbial communities revealed significant adaptation to phenolic compounds in the environment, particularly the phenol and benzoate degraders. Distribution of phenol degraders showed remarkable similarity with the heterotrophic, lipolytic and denitrifying bacterial distribution pattern. The biodegradation potential rose throughout the rivers Kohtla and Purtse revealing a high natural selfpurifcation process. Correlation of environmental variables and bacterial groups was shown. Substrate utilization patterns as recorded with the BIOLOG GN system was used to assess metabolic dynamics of microbial communities and classifying the sampling sites according to their degradative potential.