The largest river in the Caucasus, Kura, originating from the mountainous areas of Eastern Anatolia of Turkey the basin of which is connected with the territory of 5 states (Turkey, Armenia, Georgia, the Islamic Republic of Iran and Azerbaijan) from olden times has been subjected across the whole flow (1500 km) in varying degree to the anthropogenic influences. At the same time, none of the states located in its basin considers Kura as a major and irreplaceable source of drinking water for more than 80% of the population, agriculture and industry, as in Azerbaijan. Therefore, considering the vital importance, Kura and the reservoirs of its basin are systematically studied by us since 1956 and it continues to this day during all the seasons and years. The complex microbiological studies in the middle of Kura and in the cascade of reservoirs created in different years were started in the second half of the 50-ies of the last century. It was detected that an intensive (with increasing year-by-year rate) pollution of Kura begins in its middle part at the territory of Georgia.