A unique combination of temporal and spatial measurements provides a description of an extraordinarily large upwelling event in Lake Tahoe, CA-NV. The 4 d event, which engulfed half of the lake's surface and had an amplitude of 500 m, was recorded with in situ and space-borne instruments. The vertical mixing that ensued, was characterized by a large transfer of heat across the thermocline, resulting in the replacement of the distinct two-layer thermal structure by a diffuse, temperature gradient. Prior to the event, mixing energy due to the cooling flux at the surface was two orders of magnitude larger than the mixing energy associated with the wind. This dominance by cooling yielded the two-layer structure. During the event, wind energy was of similar magnitude to the cooling energy. The large bottom velocities that were produced at the end of the event were sufficient to re-suspend sediment into the water column.