What is the largest lake in the world?

By surface area the Caspian Sea is the largest inland body of water on Earth at about 143,000 square miles, larger than Germany. Whether it is a lake or a sea is not merely semantic: under international law, seas and lakes are governed by different frameworks for dividing resources, and the five bordering states spent decades disputing the classification because the seabed holds substantial oil and gas. A 2018 convention established a hybrid legal status rather than resolving the underlying question. Its water is brackish, roughly a third as salty as ocean water, and it is a remnant of an ancient sea that became landlocked.

Among unambiguous freshwater lakes, Lake Superior is the largest by surface area at about 31,700 square miles. But volume tells a different story: Lake Baikal in Siberia, though smaller in area, is by far the deepest lake in the world at over 5,300 feet and contains roughly 20 percent of the planet's unfrozen surface fresh water, more than all five Great Lakes together. Baikal is also among the oldest lakes on Earth at roughly 25 million years, which has allowed a remarkable degree of endemic species evolution, including the world's only exclusively freshwater seal.

Two cautionary cases sit alongside these records. The Aral Sea in Central Asia was once the fourth largest lake in the world and has lost the overwhelming majority of its volume since the 1960s after Soviet irrigation projects diverted its feeder rivers, leaving ships stranded in desert and a public health crisis from exposed contaminated seabed. Lake Chad in Africa has shrunk drastically over recent decades from a combination of drought, climate change, and water extraction, with serious consequences for the tens of millions who depend on it. Both are frequently cited as the clearest visible examples of human-caused change to major water bodies.