Abstract
Climate change and transboundary water use issues have a significant impact on the lower reaches of the Syrdarya River. This study analyzes the changes in the river's flow regime, the deterioration of water quality, and the impacts of these processes on the ecosystem. Since more than 90% of the river’s flow is formed outside Kazakhstan (in Kyrgyzstan, Uzbekistan, and Tajikistan), special attention is given to transboundary water management challenges. The construction of the Shardara reservoir and the Koksaray counter-regulator has drastically altered the flow regime, while large-scale water withdrawals for agriculture, especially during the summer, have caused water shortages. As a result, the seasonal distribution of runoff has changed, negatively affecting the ecosystem of the lower reaches. It has been observed that, in the long-term hydrological dynamics of the lower Syrdarya, water availability sharply declined during the period 2017...2024. Water mineralization and pollution levels exceed permissible standards. In terms of water quality, the pollution level of the Syrdarya river is classified as class IV (moderately polluted). This situation underscores the need to introduce the concept of environmental flow and ensure its practical implementation in water resource management. The newly adopted Water Code of the Republic of Kazakhstan and the Water Resources Management Concept for 2024...2030 are expected to serve as the foundation for positive changes in this field.