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Lake Baikal is the oldest lake in the world. It is home to approximately 1,700 to 1,800 endemic plant and animal species," said Jennifer Castner of Pacific Environment's Russia program. Additionally, it holds 20 percent of the world's fresh water, due to the lake's depth.

Interesting fact

Maximum depth: 5,354 feet (1,632 meters)

There are 27 mostly uninhabited islands in Lake Baikal, according to Lake Baikal.org. The largest is 45-mile-long (72 km) Olkhon, on which there are villages. About 1,500 people live there. More than 300 streams and rivers feed into Lake Baikal, but the Angara River is the only outlet. It carries out about 60 cubic km (15.8 trillion gallons) of water per year into the Yenisei River. Eventually the water makes its way to the Arctic Ocean.

The Selenga River is the largest source of water coming into Lake Baikal. Flowing north from Mongolia, it contributes nearly 50 percent of the lake's water. Like Lake Baikal, the Selenga Delta is internationally recognized for its biodiversity and importance, according to the Ramsar Convention.

Lake Baikal is the only very deep lake to have oxygenated water at its lowest depths, like the ocean, according to a 2009 article in BioScience. Additionally, the earth under Lake Baikal is heated. The cause of the heat is unknown.

Lake Baikal is considered one of the clearest lakes in the world, according to CNN Traveler. During the summer, when the lake is full of melted ice from the Siberian mountains, it is sometimes possible to see more than 130 feet (39 m) down. The stunning clarity is the result of the melted ice's purity, plankton that eat floating debris and a lack of mineral salts in the lake.

Lake Baikal may be warmer than other parts of Siberia, but in the winter it still gets very cold. The average air temperature in winter is minus 6 F (minus 21 C). Despite its size, Lake Baikal freezes over in the winter and usually melts in May or June, according to LakeBaikal.org. The ice can be up to 6 feet (2 m) thick. In the summer, the average air temperature is 52 F (11 C). The water temperature in August is around 50 F (10 C).