Our paper discusses research into primary production of water discharged from a power plant with 1,600 MW capacity in conjunction with select hydrochemical indicators. It was proven that, on average, the temperature of spent cooling water was higher by 6.3ºC than the temperature of natural waters. Oxygen conditions were favorable for water biocenoses, whereas concentrations and transformations of biogenic elements were characteristic for eutrophized waters. Average annual primary production of spent cooling water equaled 0.300 mgC·dm^-3·h^-1 and exceeded by 27% primary production of water that had not been subject to thermal pollution.