Dissolved oxygen (DO) plays an important role in the biogeochemical cycle, the evolution of ecosystem structure and function. It is also a sensitive indicator of physical and biogeochemical changes in aquatic ecosystems. Previous studies suggested that most of the water source reservoirs or lakes could form a metalimnetic oxygen minimum (MOM) during the thermal stratification period in summer and autumn. Furthermore, an anoxic and anaerobic conditions can be induced in this region. High density gradient of metalimnion, the aggressive consumption of DO by the degradation of algae and organic matters, and the respiration of microorganisms are considered as the main contributors. MOM restricts the diurnal and nocturnal migration patterns of zooplanktons, disturbs the vertical distribution of invertebrates and fish in the reservoirs. The existence of MOM will destroy the ecological distribution of water bodies and lead to the abnormal death of organisms. In addition, MOM will significantly change the dynamics of greenhouse gases (CH₄ and CO₂) in water and affect the quality of water supply as well. Recently, series of studies about MOM have been published, but no comprehensive review is reported. In this paper, MOM is comprehensively discussed from five aspects, including the research history, causes, ecological risks, water quality responses and control measures. The future research directions and fields are also discussed in order to promote the relevant research of MOM, to ensure the ecological balance of lakes and reservoirs and the water quality of water supply.