This paper outlines the influences of water resource development on the ecology of the arid regions of north-west China. The Hei River basin served as a case study. Water resources in the arid zones of north-west China, which have an inland hydrological basin as their unit, form relatively independent ecosystems. In such basins, surface runoff flowing out of the mountain reaches of rivers become the only water source available for the middle and lower reaches. Important changes in the hydrological conditions and ecology of the Hei River basin have taken place in the last 50 years. The discharge in the lower reaches of the river has decreased significantly and more than 30 tributaries as well as terminal lakes have dried up. Such hydrological changes resulted in a marked degradation of the environment, secondary salinization and desertification of land in the entire basin. Such changes are mainly attributable to the misuse of water resources. Keywords: Hei River basin, water resources development, hydrological change, ecology, degradation.