Deep Lake is a small hypersaline lake in the Vestfold Hills region of Antarctica.
Deep Lake's surface temperature on average ranges from -16 to 12 ðC, with only a few meters at the lake's surface exceeding 0 ðC for a few months of the year during the austral summer. Lake water temperatures can fall as low as -20 ðC in winter, however the lake's water column is able to remain free of ice year-around due to the high salinity (~270 g/L) of the lake water. The archaeon Halorubrum lacusprofundi was first isolated from Deep Lake in the 1980s and is the first archaea domain member to be isolated from a cold environment. It has a max depth of .