The construction of human made reservoirs includes flooding of a large area of the terrestrial landscape, deeply altering the natural carbon dynamics of the watershed. Amongst the processes affected, some of major concern are GHG production, consumption, and emissions. While our current knowledge about these is mostly from assessments in temperate and boreal biomes, reservoir constructions are growing fast in the tropics. Therefore, we are interested in exploring how the presence of a reservoir influences the dynamics of carbon, particularly CO2 and CH4, and the associated microbial communities in the tropical reservoir Batang Ai (Malaysia).