The Don River is the main river system in the Azov Sea Basin. The average water flow is about 28 km3 per year. The biota of the river system is characterized by a rich vegetation and animal life including aquatic organisms. Great changes in the environment of the River Don have been observed since the period 1930 - 1960, when large numbers of dams were constructed, diverting water flow for heavy industry, energy production, agriculture and other uses. Simultaneously, water pollution increased. As a consequence, the biota of the region has been impacted negatively. Some of the detrimental effects are the decreased reproduction of commercially important fish species, and the much reduced catches of these fish. This report reviews the changes that have occurred in the ecosystem of the River Don Basin.