Methane (CH₄) and carbon dioxide (CO₂) fluxes at the sediment-water interface were studied during autumn in three reservoirs in Poland. The theoretical diffusive fluxes of dissolved pore-water carbon gases to the overlying water ranged from 0.16 mg·m^-2d^-1 to 3.84 mg·m^-2d^-1 and from 20.68 mg·m^-2d^-1 to 99.88 mg·m^-2d^-1 for methane and carbon dioxide, respectively. The comparison between the diffusive fluxes of methane at the sediment-water interface and its fluxes at the water-atmosphere interface showed that an ebullition is probably the major pathway for CH₄ transport from the sediment to the atmosphere. The fluxes of CO₂ at the sediment- water interface were considerably lower than its fluxes at the water-atmosphere interface. This indicates that most CO₂ is generated in the water column, whereas only a small portion originates from sediments.