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There are several ways to define the largest lake in the world: volume and surface area as well as water type. By volume the Caspian Sea is the largest saltwater lake with a volume of 78,700 cubic km. Lake Baikal is the largest freshwater lake with a volume of 23,000 cubic km(20% of the world freshwater). Lake Superior is the largest freshwater lake in the world by surface area at 82,103 square km, but the Caspian Sea again comes into to play as the largest saltwater lake by surface area at 370,886 square km. Below is a short paragraph about each lake.
The Caspian Sea is the largest enclosed body of water on Earth and is classified as a lake and as a sea. It is in an endorheic basin(no outflow of water). It has a salinity of 1.2%, which is about 1/3 that of an ocean. It is a remnant of the ancient Paratethys Sea and became landlocked about 5.5 million years ago. Due to the current inflow of fresh water, the Caspian Sea is a fresh-water lake in its northern portions, but the Garabogazkol embayment routinely exceeds oceanic salinity by a factor of 10.
As the most voluminous freshwater lake in the world, Lake Baikal contains roughly 20% of the world’s surface fresh water. At 1,642 m Lake Baikal is the deepest and clearest lake in the world. At more than 25 million years old, Baikal is also the world’s oldest lake. It was formed as an ancient rift valley with a surface area of 31,722 square km. It is home to more than 1,700 species of plants and animals, two thirds of which are unique to the area.
Lake Superior is the largest of the five North American Great Lakes. It has a surface area of 82,413 square km(the size of some countries). It has a maximum length of 563 km and a maximum breadth of 257 km. Its average depth is 147 m with a maximum depth of 406 m. The lake contains 12,100 cubic km of water. There is enough water in Lake Superior to cover the entirety North and South America with 30 cm of water.
As with many things in science, especially geography, there is more than one answer to which is the largest lake in the world. At least now, you can give an educated answer the next time it comes up.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.