Lake Baikal is the world's oldest lake, at 25 million years (possibly older), and deepest, averaging 744.4 metres (2,442 ft).

Located in the south of the Russian region of Siberia, between Irkutsk Oblast to the northwest and the Buryat Republic to the southeast, it is the most voluminous freshwater lake in the world, containing roughly 20% of the world's unfrozen surface fresh water.

An octopus is filmed by the National Oceanic and Atmospheric Administration ship Okeanos Explorer and its robotic sub. (Photo by National Oceanic and Atmospheric Administration)

Long row of shiny new Flying Fortresses, part of huge reserves being built up in Britain for D-Day, stands by to be flown to combat units as replacements, May 25, 1944. (Photo by AP Photo)

A pedestrian leaps across a flooded portion of the La Paz and Seventh Street intersection as a winter storm arrived, Thursday, December 6, 2018 in Victorville, Calif. The second round of a fall storm dumped snow and rain that jammed traffic on Southern California highways and loosened hillsides in wildfire burn areas on Thursday. (Photo by James Quigg/The Daily Press via AP Photo)

Copperhead ridden by Harry Cobden falls during the RSA Insurance Novices' Chase (Grade 1) at Cheltenham Racecourse on March 11, 2020 in Cheltenham, England. (Photo by Tom Jenkins/The Guardian)

A person stands next to the skyline of lower Manhattan on the opening day the Edge NYC, an outdoor observation deck on the 100th floor of 30 Hudson Yards on March 11, 2020 in New York City. (Photo by Gary Hershorn/Getty Images)