The following bacterial genera were identified in the sediment samples from the Uh and Latorica rivers Citrobacter, Proteus, Pseudomonas, Escherichia, Enterobacter, Enterococcus, Staphylococcus and Salmonella. Both the rivers are frequently polluted by crude oil substances and by municipal waste waters. We observed growth development of bacteria in collected samples and inoculation ones by standard strains Escherichia coli 324/70 and Pseudomonas aeruginosa Ps 168/79. A one-year period i.e. from September 1994 to September 1995, showed a high degradation of those substances, ranging from 65.5% to 96.1%. The obtained results indicate an important role of both natural as well as other conditions in biodegradation processes. Important is also the presence of suspended soil particulars as well as particulars of municipal wastewaters in water environment because they form a suitable condition for growth developing of microorganisms.