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The inland water system is a key conduit in transporting carbon from land to ocean, but this conduit is not a neutral pipeline because it releases greenhouse gases into the atmosphere and also stores carbon in sediment. Currently, the role of inland waters in the global carbon cycle is modified and complicated by the huge number of reservoirs that are associated with climatic alteration due to their carbon sequestration and greenhouse gas emission functions. Moreover, reservoirs are distinct from natural rivers and lakes in various ways, promoting the emission of greenhouse gases from their surfaces and carbon accumulation in sediment through high sedimentation rates and larger ratios of watershed areas to reservoir areas. Consequently, their contributions to the global carbon cycle will increase in the coming decade as a result of an increase in the number of reservoirs. This assessment (1) demonstrates that reservoirs play a significant role in carbon burial and greenhouse gas emissions, (2) defines factors that influence the carbon budget of reservoirs, and (3) explains how reservoirs affect global climatic change. According to previous findings, reservoirs could serve as carbon sinks or sources, depending on the age, location, and climate of the given reservoir. Further, the magnitude of carbon burial and greenhouse gas emissions in reservoirs depends on productivity, land use, geology, water body type, and watershed morphometry. So far, few studies have examined both carbon storage and greenhouse gas emissions in reservoirs, and many efforts to quantify burial and emissions have been compromised by limited data availability. In this review, we mainly focus on recent literature on carbon burial and greenhouse gas emissions in reservoirs and global estimates of terrestrial carbon input to inland waters.