The largest freshwater reservoir on Earth, defined by the volume of accessible, liquid surface water, is Lake Baikal. Located in Siberia, Russia, this immense body of water holds approximately one-fifth of the world’s unfrozen surface freshwater supply. Its volume alone surpasses that of entire systems of major lakes elsewhere in the world.
Physical Dimensions of the World’s Largest Lake
Lake Baikal is the largest reservoir due to its profound depth, not its surface area. While it is the world’s seventh-largest lake by surface area, it is the deepest lake on the planet, with a maximum recorded depth of 1,642 meters (5,387 feet). This makes it significantly deeper than any other continental body of water.
This immense vertical scale allows the lake to store an extraordinary volume of water, estimated at 23,615 cubic kilometers. This volume is greater than the combined total of all five North American Great Lakes, which cover a much larger surface area. The lake is also the world’s most ancient, dating back 25 to 30 million years.
Its longevity and geological setting allowed it to accumulate vast depth and water volume over eons. The average depth of Lake Baikal is 744 meters, which exceeds the maximum depth of many other large lakes. These extreme dimensions define it as the planet’s most substantial freshwater reserve.
Unique Biodiversity and Geological Formation
The massive volume and extreme age of Lake Baikal result from its unique geological origin as an active continental rift valley. It is situated within the Baikal Rift Zone, where the Earth’s crust is slowly pulling apart. This tectonic activity created the deepest continental rift on the planet.
The rift continues to widen by a few millimeters each year, deepening the basin and contributing to the lake’s longevity. This combination of great depth and continuous geological change has provided a stable environment for evolution over millions of years.
This prolonged isolation has resulted in endemism, where life forms evolve exclusively within the lake’s ecosystem. Over two-thirds of the more than 2,600 identified plant and animal species found here are endemic, existing nowhere else on Earth.
Examples include the Baikal seal (nerpa), the only exclusively freshwater seal species. The food web is supported by the tiny Epischurella baikalensis copepod, an endemic crustacean that acts as a natural filter, contributing to the water’s clarity. Other unique species include the omul whitefish and the golomyanka, a translucent fish.
Context in Global Freshwater Distribution
Understanding Lake Baikal’s magnitude requires placing it within the context of the Earth’s total water supply, which is predominantly saline ocean water. Only 2.5% of the planet’s total water is freshwater, and most is not readily accessible.
Approximately 70% of the world’s freshwater is locked away in glaciers and permanent snow cover; the rest is groundwater. Less than 1% of the world’s freshwater supply is in liquid surface forms like lakes and rivers.
Lakes hold nearly 87% of this surface water. Lake Baikal’s share of 20% to 23% of the world’s unfrozen surface freshwater demonstrates its significance.
This single Siberian lake contains more accessible liquid freshwater than entire continents possess in their lake systems. The North American Great Lakes are geographically extensive but collectively hold less water volume than Baikal.
Threats to the Lake’s Ecosystem
Despite its enormous size and UNESCO World Heritage status, Lake Baikal faces significant environmental pressures. One major concern is industrial pollution, particularly from historical sources like the Baikalsk Pulp and Paper Mill, which discharged wastewater directly into the lake.
Although the mill has closed, current threats include discharge from the Selenga River, which carries toxic substances from upstream urban and industrial centers. Inadequate sewage treatment, exacerbated by increasing mass tourism, is leading to nearshore eutrophication.
This nutrient overload stimulates the growth of non-native, toxic algal blooms. These blooms choke out endemic filter-feeding species and contribute to the decline of Baikal’s unique sponges.
Climate change presents another serious threat, with surface water temperatures rising significantly. Warmer water holds less dissolved oxygen, stressing cold-adapted endemic species and making them susceptible to disease and invasive organisms. Furthermore, the thawing of surrounding permafrost risks releasing additional trapped industrial toxins into the watershed, compounding the existing pollution problem.