Caspian Sea: the largest lake in the world
The Caspian Sea is the biggest landlocked water on the planet. It sits where Europe meets Asia. People call it a sea, but it has no outlet and only a little salt - it acts like a mix between a sea plus a lake. Five countries border it - Kazakhstan, Turkmenistan, Iran, Azerbaijan besides Russia. The water runs 745 miles from top to bottom and covers about 143,200 square miles, an area close to that of Japan.
The basin formed over millions of years. It did not appear because ocean plates pulled apart - it is a leftover piece of the old Tethys Sea. Plate movements but also climate change cut the water off from the open ocean. The Caucasus or Alborz mountains rose and trapped the water inside. Ice ages as well as warm spells later raised and lowered the water level or changed the amount of river water that entered the basin.
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The water holds a middling level of salt - about 12 grams of salt in every thousand grams of water. That is saltier than a lake but less salty than an ocean. The salt level stays moderate because no ocean water flows in and large rivers - the Volga, Ural next to Kura - pour in fresh water. The Volga sends in the largest share of that fresh water also so controls both salt levels and living conditions in the northern part.
The mix of salt next to fresh water gives the basin a wide variety of life. Native fish include sturgeon, valued for caviar and the only sea mammal is the Caspian seal. Damaged marshes plus oil and gas work now endanger those species. The United Nations Environment Programme but also other groups run projects to protect the fragile habitat.
The region is a major source of income because of oil and gas beneath the seabed. Offshore rigs pump crude as well as crews still catch sturgeon for caviar. Both industries feed the economies of the five coastal states.
