The paper aims to evaluate hydrochemical composition of the Chernaya River waters, which is the major supplier of fresh water in Sevastopol, as well as to assess the influence of the river runoff on the ecological state of Sevastopol Bay. Flowing from the Chernorechenskoye Reservoir, the Chernaya River crosses the Baydar Valley and on its way takes in several tributaries, not having passed through the reservoir geochemical filter. Then it loses the most of its flow at several water intakes near the village of Khmelnitskoe and turns into a stream. The stream again becomes a relatively full-flowing river after the inflow of circulating water from the treatment facilities near the village of Sakharnaya Golovka, and finally, it discharges into Sevastopol Bay near the Inkerman basin. In order to investigate the transformation of the river waters hydrochemical composition as it moves from the Chernorechenskoye Reservoir to the river mouth, graphs of average concentration for some hydrochemical elements for four hydrological seasons 2012-2023 were constructed for 10 stations located on the river and two conditional stations in the water area of the bay (averaged data for the Inkerman basin and 30 stations of the bay). The waters of the Chernorechenskoye Reservoir and Chernaya River were revealed to be close in composition along the length of almost the entire channel from the outlet to the water intake near the village of Shturmovooe. Further, the composition of the river waters is determined by wastewater. Directly (without taking into account wastewater), the Chernaya River supplies significant amounts of nitrates, silicic acid and ammonium to Sevastopol Bay, but not phosphates, which come with the wastewater.