Lake Baikal, in southern Siberia, Russia, is the deepest lake on Earth at about 1,642 metres and the largest by volume of fresh water, holding roughly 23,600 cubic kilometres, around a fifth of all the unfrozen fresh water on the planet's surface. At an estimated 25 to 30 million years old, it is also the oldest lake still in existence, and so many of its plants and animals live nowhere else that UNESCO listed it as a World Heritage Site in 1996.
How Deep Baikal Goes, and How Much Water It Holds
Start with the number that makes Baikal unique. Its deepest sounding, about 1,642 metres, lies in the central basin, off the western shore between Olkhon Island and the Ushkany Islands. The lake surface sits around 456 metres above sea level, so the deepest point of the lake bed is roughly 1,180 metres below sea level, making it one of the lowest exposed or submerged continental depressions anywhere.
Depth on that scale turns a long, narrow lake into an enormous reservoir. Baikal is about 636 kilometres long and at most around 80 kilometres wide, with a surface area of roughly 31,500 square kilometres. That is less than half the area of Lake Superior, yet Baikal holds about 23,600 cubic kilometres of water, more than all five North American Great Lakes put together. Estimates of its share of the world's unfrozen surface fresh water range from about 20 to 23 percent, depending on how rivers, reservoirs and smaller lakes are counted.
Roughly 330 rivers and streams flow into the lake. The largest by far is the Selenga, which rises in Mongolia and enters Baikal from the southeast through a broad delta; it supplies about half of all inflow. Only one river leaves: the Angara, which drains from the southwestern tip near the village of Listvyanka, runs north past Irkutsk and later joins the Yenisei on its way to the Arctic Ocean.
A Rift Pulling Siberia Apart
Baikal is deep because it sits in an active continental rift, the Baikal Rift Zone, where the Eurasian Plate and the smaller Amur Plate are slowly moving apart. As the crust stretches, a long block between parallel faults drops down, forming a trough called a graben. The water fills only the top part of it. Beneath the lake bed lies sediment that seismic surveys estimate at up to about 7 kilometres thick in places, so the bottom of the rift itself sits somewhere around 8 to 9 kilometres below the surrounding mountains.
The rift started opening roughly 25 to 30 million years ago, which is why Baikal is far older than glacial lakes such as those of Scandinavia or Canada, most of which formed after the last ice age, about 10,000 to 15,000 years ago. Baikal has survived because the basin keeps deepening faster than rivers can fill it; GPS measurements show the two sides separating by a few millimetres per year.
The activity is visible. The region has frequent earthquakes, and hot springs rise along the faults at places such as Goryachinsk on the eastern shore and Khakusy in the north. In January 1862 a strong earthquake caused part of the Selenga delta to subside, and an area of steppe of roughly 200 square kilometres sank beneath the water to form Proval Bay.
Nerpa, Golomyanka and Baikal's Endemic Species
Long isolation, cold oxygen-rich water and an age of tens of millions of years have produced one of the richest freshwater ecosystems known. Scientists have described several thousand species of plants and animals in and around the lake, and for the animals the share found nowhere else is usually estimated at around 80 percent. Most of these are invertebrates: Baikal has hundreds of endemic species of amphipods, small crustaceans that scavenge on every part of the lake floor, as well as endemic flatworms, snails and freshwater sponges such as Lubomirskia baicalensis, which forms green, branching colonies on rocks in the shallows.
The animal most people associate with the lake is the nerpa, or Baikal seal (Pusa sibirica), one of only a few seals that live entirely in fresh water. It is small for a seal, with adults around 1.1 to 1.4 metres long, and it is closely related to the Arctic ringed seal. How its ancestors reached a lake more than 1,500 kilometres from the nearest ocean is still debated; the usual explanation is that they swam up the Yenisei and Angara river systems during a cold period when the waterways connected. Females give birth in late winter in snow dens on the ice, and recent population estimates exceed 100,000 animals.
The seal's main food is the golomyanka, a pair of endemic fish species in the genus Comephorus. They are pale and nearly translucent, have no swim bladder, and a large part of their body weight is oil. Taken together, golomyanka are thought to make up a large share of the fish biomass in the lake.
At the base of the food web is a tiny endemic copepod, Epischura baikalensis, which filters algae and bacteria and is credited with much of the lake's clarity. Higher up sits the omul (Coregonus migratorius), a whitefish that has been a staple of local diets for centuries and is sold smoked at the markets of Listvyanka. Its stocks fell so far that Russia banned commercial omul fishing from October 2017.
Shamans, Railways and a Paper Mill: People on the Shore
The Buryats, a Mongolic people, and the Evenks lived around Baikal long before Russians arrived, and the lake remains sacred in Buryat tradition. Olkhon Island, at about 730 square kilometres the largest island in the lake, is a centre of Siberian shamanism. Russian Cossacks under Kurbat Ivanov reached the lake in 1643, and Irkutsk, founded as a fort in 1661 on the Angara about 65 kilometres from the lake, grew into the administrative capital of eastern Siberia.
The lake was an obstacle for the Trans-Siberian Railway. Until a line around the southern shore was finished, trains were carried across by the icebreaking ferry Baikal. During the Russo-Japanese War of 1904, when the ice was too thick for the ferry, tracks were laid directly across the frozen lake. The Circum-Baikal Railway, completed in 1904 and opened to through traffic in 1905, hugs the cliffs between Slyudyanka and Port Baikal through dozens of tunnels and galleries.
The Irkutsk hydroelectric dam on the Angara, completed in the 1950s, raised the level of the lake by roughly a metre,. The best-known conflict over the lake was the Baikalsk Pulp and Paper Mill, known by its Russian initials BTsBK. Built on the southern shore and opened in 1966, it discharged effluent into the lake for decades and became the focus of one of the Soviet Union's first public environmental campaigns. It closed in 2008, reopened in 2010, and shut for good in 2013; cleaning up its sludge ponds has continued since. Today's pressures are more diffuse: untreated sewage from shoreline settlements, mats of Spirogyra algae in shallow bays, and die-offs of endemic sponges.
Visiting Baikal: Winter Ice or Summer Water
Most visitors begin in Irkutsk, which has an international airport and a station on the Trans-Siberian, then travel about 70 kilometres by road to Listvyanka at the source of the Angara. Further north, Olkhon Island is reached by a ferry across the strait known as the Olkhon Gate, and its main village, Khuzhir, sits beside Cape Burkhan and Shaman Rock.
The two seasons give quite different trips. In winter the lake usually freezes from early January, starting in the shallow north, and the ice lasts until around May. It typically reaches about 1 to 1.5 metres thick, which is enough for official ice roads to Olkhon to open for cars. The low snowfall leaves large areas of clear ice through which you can see bubbles of trapped methane and the water below, and the shoreline grottoes on Olkhon fill with icicles. The site's own guide to how Baikal's winter ice forms covers the cracking and bubbles in more detail.
Summer, from late June to early September, is the season for hiking the Great Baikal Trail, kayaking, taking the Circum-Baikal tourist train, or catching a hydrofoil to the Barguzin coast and the warm springs of the north. The open lake stays cold, rarely much above 10 to 12 °C at the surface even in August, though shallow bays such as Chivyrkuy Bay and the Maloye More strait between Olkhon and the mainland warm up enough for swimming.
Baikal vs Tanganyika vs Superior
Baikal is often compared with Lake Tanganyika in East Africa and Lake Superior in North America, and the comparison shows what depth does. Tanganyika is the second deepest lake, at about 1,470 metres, and also a rift lake, formed by the East African Rift. It is slightly longer than Baikal at about 670 kilometres, holds roughly 18,900 cubic kilometres, and is shared by Tanzania, the Democratic Republic of the Congo, Burundi and Zambia. The big difference is oxygen: Tanganyika is permanently layered, so most of its deep water has no dissolved oxygen and supports little life, while Baikal is oxygenated to the floor.
Lake Superior is the opposite case. It has the largest surface area of any freshwater lake, about 82,100 square kilometres, more than two and a half times Baikal's. But it was carved by glaciers and is relatively shallow, with a maximum depth of about 406 metres, so it holds only around 12,100 cubic kilometres, roughly half of Baikal's volume. The site's Baikal and Superior comparison covers that pairing in more depth.
By volume the order is the same: about 23,600 cubic kilometres for Baikal, 18,900 for Tanganyika and 12,100 for Superior. The Caspian Sea is larger than all three in both area and volume, but its water is brackish, so it is normally ranked separately. For how the remaining lakes on the list compare, see the ranking of the deepest lakes in the world, or read about the rest of Siberia's landscape in these facts about Russia's geography.