The analysis of the degree of pollution of aquatic objects in the Balti urban ecosystem after CODCr and COB5 shows that according to the values of these indices (mg/l), on the first place after the degree of pollution is water r. Răut, str. Locomotivelor, bridge, CODCr (134.8), and BOD5 (27.0). According to the values of both indices, the water quality class is (V) (highly polluted). Subsequently, the Orășenesc pond, city Bălți, CODCr (133.5) and BOD5 (26.7), the quality class is (V) (highly polluted); on the third place is the Copaceanca river, a tributary of the Răut river, city Bălți, (route) CODCr (124.5), and BOD5 (24.9), quality class (V) (highly polluted); follows the Hunters and Fishermen‘s Pond, city Bălți, CODCr (121.9) and BOD5 (24.5), the water quality class is (V) (highly polluted), and the fifth place – Răut river, upstream (confluence with the Copaceanca tributary), city Bălți, CODCr (116.1) and BOD5 (23.2), the water quality class is (V) (highly polluted). These data demonstrate the consistency of surface water pollution with light organic (BOD5) and hard to degrade (CODCr) pollutants. For the first five aquatic objects, the quality class according to both indices demonstrates a very high degree of pollution of aquatic objects (class V). Subsequently, the consequence of reducing the degree of pollution is: after CODCr water r. Răut, downstream biological treatment plant (BTP) Bălți, CODCr (87.4), (water quality class is (IV), polluted) and after BOD5 (11.4), is class (V) (highly polluted). According to CODCr (80,2), the river Răut, upstream of BTP, Bălți, the quality class is (IV), polluted, and after BOD5 (10,8) the quality class is (V), very polluted. For r. Răut, Dobruja tributary, Sorocii street, bridge, town, Bălți, CODCr (77.4), the quality class is (IV), and for BOD5 (17.5), the third quality class. For water r Răuțel (entrance to Bălți), CODCr (73.5), quality class is (IV), polluted, and BOD5 (14.7), quality class is (V), very polluted. Downstream BTP, Floresti, CODCr constitutes (36.0), class (IV) quality (polluted), and BOD5 for the same water is (7.9), class a (V) quality (highly polluted). Răut, upstream BTP, Floresti, CODCr is of (32.9) quality class (IV) (polluted), and BOD5 (7.6), quality class (V), very polluted. Is established, for water r. Flămânda, the tributary r. Răut, town Bălți, CODCr is less than 30 mgO2/l, class (III) quality, and for BOD5 (1,2), mgO2 / l, class (I) quality (clean water). The experimental results indicate a high degree of surface water pollution for virtually all aquatic objects located in the Balti urban ecosystem. The high degree of water pollution is caused by the operation of industrial enterprises and anthropogenic household activities. For the waters of the Răut River outside the urban ecosystems of Bălți and Floresti, the main sources of pollution are inadequately treated water at BTP Balti and Floresti.