Four lake-floor seeps have been studied in the gas-hydrate area in Lake Baikal's South Basin by using side-scan sonar, detailed bathymetry, measurements of near-bottom water properties, heat-flow measurements, and selected seismic profiles in relation to results from geochemical pore-water analysis. The seeps at the lake floor are identified as methane seeps and occur in an area of high heat flow, where the base of the gas-hydrate layer shallows rapidly toward the vent sites from ∼400 m to ∼150 m below the lake floor. At the site of the seep, a vertical fluid conduit disrupts the sedimentary stratification from the base of the hydrate layer to the lake floor. The seeps are interpreted to result from local destabilization of gas-hydrate caused by a pulse of hydrothermal fluid flow along an active fault segment. This is the first time that methane seeps and/or mud volcanoes associated with gas-hydrate destabilization have been observed in a sublacustrine setting. The finding demonstrates the potential of tectonically controlled gas-hydrate destabilization to cause extreme pore-fluid overpressure and short-lived mud volcanism.