On February 27 or 28, Lake Tahoe flipped or, more correctly, it fully mixed vertically from top to bottom. Full mixing is an annual event in shallower lakes, however for Tahoe and its 1,640-foot depth, it is a less common occurrence. Lake Tahoe last mixed during the 2018-19 winter.
How do we know it flipped? TERC researchers are on the lake every week sampling the water quality, the phytoplankton, and the overall health. Researchers also maintain instruments in the lake, which take measurements every few minutes.