Abstract:Total dissolved gas (TDG) supersaturation caused by dam spills may lead to gas bubble disease and even fish mortality, resulting in serious negative impacts on the aquatic ecosystem. With more and more high dams put into operation in recent years, the problem of total dissolved gas supersaturation has become an important ecological risk restricting the safe operation of high dam discharge in China. By combining literature analyses and the authors' research experience in the field, the problem of dissolved gas supersaturation, its effect on fish and the mitigation measures were retrospected. First, for the protection needs of endemic fish in the upper reaches of the Yangtze River, the negative effect of TDG supersaturation and the tolerance ability of fishes to TDG supersaturation were reviewed. The mechanism of TDG supersaturation and its simulation technology was revealed from the perspective of the generation and dissipation process. The mitigation technology and its engineering application were described from the engineering measures, dispatching measures, and ecological function utilization measures. According to the ecological safety demand of high dam discharge in China, the research trend at home and abroad was analyzed. It was proposed that the current key problems and challenges mainly include further revealing the mechanism of TDG supersaturation, improving the accurate and advanced prediction methods, strengthening the engineering feasibility study of TDG mitigation technology, implementing the cascade muti-object optimal dispatching based on TDG supersaturation mitigation, and promoting the establishment of fish tolerance standards to TDG supersaturation. The effort of this paper aims at providing scientific reference and guide for the solution of TDG supersaturation and guarantee the ecological safety of high dam operation.