The deepest lake in the world is Lake Baikal in southern Siberia, Russia. Its maximum measured depth is approximately 1642 metres, making it substantially deeper than any other lake on Earth. Lake Baikal is also remarkable because its great depth combines with an extensive surface area to produce an enormous water volume. It contains roughly 23000 cubic kilometres of water, representing about one fifth of the worlds unfrozen surface freshwater and more freshwater than any other lake. The lake is approximately 636 kilometres long and reaches a maximum width of about 79 kilometres. Its great depth is therefore not an isolated measurement but part of a much larger geological and hydrological system.
Lake Baikals depth results primarily from its tectonic origin. Unlike many large lakes formed mainly by glacial erosion, Baikal occupies an active continental rift zone where the Earths crust is being pulled apart. The Baikal Rift Zone contains faults and deep structural basins that have progressively developed over millions of years. Sediments have accumulated to great thicknesses on the lake floor while tectonic subsidence has maintained substantial basin depth. The lake is geologically ancient, commonly estimated to be approximately 25 to 30 million years old, although exact estimates depend on geological interpretation. Its age and continuing tectonic activity distinguish it from many comparatively young glacial lakes.
Lake Baikals maximum depth is measured from the water surface to its deepest known point beneath the lake. Depth should not be confused with elevation of the lake floor relative to sea level. Because the lake surface itself lies approximately 456 metres above mean sea level, the deepest bottom lies roughly 1186 metres below global mean sea level. This illustrates an important distinction between absolute depth and elevation.
The term maximum depth describes the vertical distance through the water column at the deepest location, whereas bathymetry describes the shape and depth distribution of the entire lake floor. Most of Lake Baikal is considerably shallower than its deepest point, so its maximum depth is a specific extreme rather than the average depth.
The lake contains an exceptional biological community, including many species found nowhere else. One famous endemic species is the Baikal seal, also called the nerpa, which is the only seal species known to live exclusively in freshwater. Other endemic organisms include numerous crustaceans, fish, sponges and microscopic species. The unusual ecology is associated with the lakes geological age, isolation, depth, water chemistry and complex circulation. The depth also creates a large vertical environment in which temperature, pressure, dissolved gases, nutrients and biological communities vary substantially. The lakes deep water remains relatively cold, while seasonal circulation helps redistribute oxygen and nutrients through much of the water column.
Lake Baikals water volume is another reason it is scientifically important. Its enormous depth combined with its broad basin allows it to hold more liquid freshwater than any other individual lake. Although the worlds ice sheets and glaciers contain vastly more freshwater overall, Lake Baikal is exceptional among unfrozen surface freshwater bodies. Its water is generally clear, cold and relatively low in dissolved minerals. The lakes famous clarity is influenced by biological and chemical processes that remove suspended material, although clarity varies spatially and seasonally. The large volume also gives the lake substantial thermal inertia, meaning that its water does not respond instantly to changes in atmospheric temperature.
Lake Baikal freezes during winter over substantial portions of its surface, despite its great depth. Ice conditions vary according to season, weather and location, with the shallow margins generally freezing earlier than deeper areas. The formation and breakup of ice influence ecological processes, light penetration, gas exchange and seasonal habitat. The lake is also important to regional climate and hydrology because it stores enormous quantities of freshwater and receives water from numerous rivers and streams while losing water primarily through its outflow, the Angara River. The surrounding catchment includes forests, mountains, wetlands and human settlements, all of which influence the lakes water quality and ecological condition.
Several other very deep lakes are sometimes confused with Lake Baikal in popular references. Lake Tanganyika in Africa reaches approximately 1470 metres, making it the second deepest lake by commonly accepted maximum depth. The Caspian Sea reaches roughly 1025 metres in its deepest southern basin. Crater Lake in the United States reaches about 594 metres and is the deepest lake in North America. These comparisons demonstrate why the word deepest must refer to maximum depth rather than surface area or water volume. A lake with a very large area can be shallower than a smaller lake formed in a tectonic or volcanic depression.
Lake Baikal is therefore the global record holder for maximum lake depth at approximately 1642 metres. Its depth is explained by active continental rifting and a long geological history rather than simply by erosion at the surface. The same geological system has produced an exceptionally large freshwater volume, unusual endemic biodiversity and distinctive physical conditions. Lake Baikal is simultaneously the worlds deepest lake, the worlds largest freshwater lake by volume and one of the oldest major lake ecosystems on Earth. These different records illustrate why lake comparisons require a clearly specified measurement such as maximum depth, surface area or volume.
