The surface-atmospheric exchange of CO2 and CH4 was measured continuously using the flux gradient approach from a beaver pond in the northern study area of the Boreal Ecosystem-Atmosphere Study between May 22 and September 19, 1994. The beaver pond was a large source of CO2 and CH4 for the entire study period. The half-hourly mean flux of CO2 and CH4 ranged from -0.498 to 1.135 mg CO2 m-2 s-1 and from -0.805 to 37.5 μg CH4 m-2 s-1, respectively, while the seasonal mean fluxes were 0.072¿0.095 mg CO2 m-2 s-1 and 1.26¿1.87 μg CH4 m-2 s-1. The beaver pond rarely took up CO2. There was a large flux of both gases during the daytime. This increase is related to the transfer of the gases rather than to specific controls on production. The total efflux of CO2 and CH4 for the 120 days of the study was 678 g CO2 m-2 and 11.3 g CH4 m-2, or 183 and 8.4 g C m-2, respectively. When the measurements ceased, the sediment temperatures were >10 ¿C, so it is reasonable to expect that the fluxes of CO2 and CH4 continued into the late fall. This indicates that the beaver pond released more than 200 g C m-2 yr-1. ¿ 1997 American Geophysical Union