The owners of Tatogga Lake Resort informed geologists of persistent flammable natural gas seepage into Tatogga Lake, British Columbia. The gas seep was sampled from anomalously unfrozen openings (UTM zone 9, 440378/6396983, NAD27) when the ice cover was generally 15 to 20 cm thick. Samples of this gas are composed of methane (98.2 %) and carbon dioxide (1.8 %). The stable carbon isotopic composition of both gases is consistent with biogenic generation and possibly slight microbial oxidation. The biogenic origin of this natural petroleum seepage suggests that the gas is not associated with crude oil stains and thermogenic petroleum systems in the Bowser Basin and underlying rocks. The seepage source strata and economic potential remain unidentified and obscured by its underwater occurrence.