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Recent studies have revealed that inland waters, such as rivers, act as an excellent source of soil-derived CO2 for the atmosphere. This flow is comparable in magnitude to that of anthropogenic CO2 release, such as fossil fuel use, playing an important part in the global carbon cycle and future climate change. Although one of the most active CO2 evasions in the world has been reported in Himalayan rivers, data on the partial pressure of CO2 (pCO(2)) remains sparse. In this study, we conducted a monthly sampling survey of the Ganges River in Bangladesh during 2011-2014 and measured the chemical composition of the river water. Both chemical weathering and dissolution of soil salt may affect seasonal variations in major ion composition in this river. The pCO(2) values were 377-1,763 mu atm, which were higher than the atmospheric level (400 mu atm). Higher pCO(2) values were observed during the rainy season, which was likely attributed to active respiration by soil or river biota. We also calculated approximate CO2 evasion rates from the river into the atmosphere. Our results suggest that water during the rainy season, which has high pCO(2), temperature, and water current velocity, releases CO2 into the atmosphere more efficiently (150 mol m(-2) yr(-1)) than that during the dry season (20 mol m(-2) yr(-1)). In addition, we collected groundwater samples in Bangladesh and observed surprisingly high pCO(2) values (4,926-101,610 mu atm). Groundwater in this area is likely to transport abundant dissolved inorganic carbon (both HCO3- and CO2) to the ocean.