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Caspian Sea: the story on HearLore | HearLore
Caspian Sea
The Caspian Sea is the world's largest inland body of water, covering an area of approximately 371,000 square kilometers, which is nearly five times the size of Lake Superior and larger than the entire country of Germany. Despite its name, it is technically a lake, yet it possesses many characteristics of a sea, including a salinity of about 1.2 percent, which is roughly one-third that of average seawater. This unique body of water is situated in both Europe and Asia, bordered by Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the southwest, Iran to the south, and Turkmenistan to the southeast. Its surface lies about 28 meters below sea level, and its deepest point reaches 1,025 meters below sea level, making it the third-lowest natural non-oceanic depression on Earth after Lake Baikal and Lake Tanganyika. The Caspian Sea is an endorheic basin, meaning it has no natural outflow to the ocean, and its water level has fluctuated dramatically over millions of years due to tectonic activity and climate changes. The name Caspian Sea is derived from the ancient Caspi people, who lived to the southwest of the sea in Transcaucasia, and it has been known by various names throughout history, including the Hyrcanian Sea among the Greeks and Persians, and the Sea of Khazars in medieval Arabic sources.
A Geological Remnant of Ancient Seas
The Caspian Sea is a remnant of the ancient Paratethys Sea, which separated from the open oceans around 5.5 million years ago during the Late Miocene epoch due to tectonic uplift and a fall in sea level. Its seafloor is composed of standard oceanic basalt, not continental granite, indicating its deep-sea origins. The basin has undergone significant changes over time, with the Caspian Sea being a comparatively small endorheic lake during the Pliocene, but its surface area increasing fivefold around the time of the Pliocene-Pleistocene transition. During warm and dry climatic periods, the landlocked sea almost dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. The Caspian Sea has experienced dramatic fluctuations in water levels over the centuries, with some Russian historians, such as Lev Gumilev, claiming that the rising of the Caspian in the 10th century caused the coastal towns of Khazaria to flood, resulting in the Khazars losing approximately two-thirds of their territory due to flooding. The sea level of the Caspian has fallen and risen, often rapidly, many times over the centuries, with the last short-term sea-level cycle starting with a sea-level fall of 3 meters from 1929 to 1977, followed by a rise of 3 meters from 1977 until 1995. Since then, smaller oscillations have taken place, and the current projection is that climate change will cause water levels to decline by up to 21 meters by 2100.
Common questions
What is the Caspian Sea and how large is it?
The Caspian Sea is the world's largest inland body of water covering an area of approximately 371,000 square kilometers. It is nearly five times the size of Lake Superior and larger than the entire country of Germany.
When did the Caspian Sea separate from the open oceans?
The Caspian Sea separated from the open oceans around 5.5 million years ago during the Late Miocene epoch due to tectonic uplift and a fall in sea level. It is a remnant of the ancient Paratethys Sea.
Which countries border the Caspian Sea?
The Caspian Sea is bordered by Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the southwest, Iran to the south, and Turkmenistan to the southeast. These five states maintain naval forces on the sea.
What species live in the Caspian Sea?
The Caspian Sea is home to six sturgeon species including the beluga sturgeon and the Caspian seal which is the only aquatic mammal endemic to the region. It also contains 160 native species and subspecies of fish with about 62% being endemic.
When was the Convention on the Legal Status of the Caspian Sea signed?
The Convention on the Legal Status of the Caspian Sea was signed by the five littoral states at the fifth Caspian Summit in August 2018 in the Kazakh port city of Aktau. The convention grants jurisdiction over 15 nautical miles of territorial waters to each neighboring country.
When did the Caspian Sea reach its lowest recorded level?
The Caspian Sea reached its lowest recorded level in July 2025 falling to less than 29 meters below sea level. This decline is calculated to decrease by 9 to 18 meters during the 21st century due to global warming and desertification.
The Caspian Sea is home to six sturgeon species, including the Russian, bastard, Persian, sterlet, starry, and beluga sturgeon, with the beluga sturgeon being arguably the largest freshwater fish in the world. The sturgeon yield roe (eggs) that are processed into caviar, a delicacy that has been highly prized for centuries. Overfishing has depleted a number of the historic fisheries, and in recent years, overfishing has threatened the sturgeon population to the point that environmentalists advocate banning sturgeon fishing completely until the population recovers. The high price of sturgeon caviar, which can exceed 1,500 Azerbaijani manats (US$880) per kilo, allows fishermen to afford bribes to ensure the authorities look the other way, making regulations in many locations ineffective. Caviar harvesting further endangers the fish stocks, since it targets reproductive females. The Caspian Sea has 160 native species and subspecies of fish in more than 60 genera, with about 62% of the species and subspecies being endemic. The lake proper has 115 natives, including 73 endemics (63.5%). Among the more than 50 genera in the lake proper, 3, 4 are endemic: Anatirostrum, Caspiomyzon, Chasar (often included in Ponticola) and Hyrcanogobius. By far the most numerous families in the lake proper are gobies (35 species and subspecies), cyprinids (32) and clupeids (22). Two particularly rich genera are Alosa with 18 endemic species/subspecies and Benthophilus with 16 endemic species. Other examples of endemics are four species of Clupeonella, Gobio volgensis, two Rutilus, three Sabanejewia, Stenodus leucichthys, two Salmo, two Mesogobius and three Neogobius. Almost 30 non-indigenous, introduced fish species have been reported from the Caspian Sea, but only a few have become established.
The Caspian Tiger and the Cheetah
The Caspian Sea region has been home to several iconic and now extinct or endangered species, including the Caspian tiger, the Asiatic cheetah, and the Asiatic lion. The Caspian tiger used to occur in northern Iran, the Caucasus, and Central Asia, but it is now extinct in the region since the 1970s. The Asiatic cheetah used to occur in the Trans-Caucasus and Central Asia, but is today restricted to Iran. The Asiatic lion used to occur in the Trans-Caucasus, Iran, and possibly the southern part of Turkestan. The endangered Persian leopard is found in Iran, the Caucasus, and Central Asia. Reptiles native to the region include the spur-thighed tortoise (Testudo graeca buxtoni) and Horsfield's tortoise. The Caspian seal (Pusa caspica) is the only aquatic mammal endemic to the Caspian Sea, being one of very few seal species that live in inland waters, but it is different from those inhabiting freshwaters due to the hydrological environment of the sea. A century ago the Caspian was home to more than one million seals. Today, fewer than 10% remain. Archeological studies of Gobustan Rock Art have identified what may be oceanic species including cetaceans from baleen whales to dolphins, and auks most likely Brunnich's Guillemot, although the rock art on Kichikdash Mountain which is assumed to depict either a beaked whale or a dolphin, it may represent the famous beluga sturgeon instead due to its size (430 cm in length). These petroglyphs may suggest potential presences of oceanic faunas in the Caspian Sea presumably until the Quaternary or even the last glacial period or antiquity due to historic marine inflow between the current Caspian Sea and either the Arctic Ocean or North Sea, or the Black Sea.
The Black Gold Capital of Baku
The Caspian Sea region is rich in fossil fuels, with oil wells being dug in the region as early as the 10th century to reach oil for use in everyday life, both for medicinal purposes and for heating and lighting in homes. By the 16th century, Europeans were aware of the rich oil and gas deposits locally. English traders Thomas Bannister and Jeffrey Duckett described the area around Baku as a strange thing to behold, for there issueth out of the ground a marvelous quantity of oil, which serveth all the country to burn in their houses. This oil is black and is called nefte. There is also by the town of Baku, another kind of oil which is white and very precious, i.e., petroleum. The world's first offshore wells and machine-drilled wells were made in Bibi-Heybat Bay, near Baku, Azerbaijan. In 1873, exploration and development of oil began in some of the largest fields known to exist in the world at that time on the Absheron Peninsula near the villages of Balakhanli, Sabunchi, Ramana, and Bibi Heybat. Total recoverable reserves were more than 500 million tons. By 1900, Baku had more than 3,000 oil wells, 2,000 of which were producing at industrial levels. By the end of the 19th century, Baku became known as the black gold capital, and many skilled workers and specialists flocked to the city. By the beginning of the 20th century, Baku was the center of the international oil industry. In 1920, when the Bolsheviks captured Azerbaijan, all private property, including oil wells and factories, was confiscated. Rapidly the republic's oil industry came under the control of the Soviet Union. By 1941, Azerbaijan was producing a record 23.5 million tons of oil per year, its Baku region output being nearly 72 percent of the Soviet Union's oil. In 1994, the Contract of the Century was signed, heralding extra-regional development of the Baku oil fields. The large Baku, Tbilisi, Ceyhan pipeline conveys Azeri oil to the Turkish Mediterranean port of Ceyhan and opened in 2006. The oil field in the Russian section of the body of water was discovered in 2005. It is reportedly the largest found in 25 years. It was announced in October 2016 that Lukoil would start production from it.
The Legal Status of the Caspian Sea
The Caspian Sea is legally neither fully a sea nor a lake, as determined by the Convention on the Legal Status of the Caspian Sea, which was signed by the five littoral states at the fifth Caspian Summit in August 2018 in the Kazakh port city of Aktau. The convention grants jurisdiction over 15 nautical miles of territorial waters to each neighboring country, plus an additional 10 nautical miles of exclusive fishing rights on the surface, while the rest is international waters. The seabed, on the other hand, remains undefined, subject to bilateral agreements between countries. While the convention addresses caviar production, oil and gas extraction, and military uses, it does not touch on environmental issues. Five states are located along about 7,000 kilometers of the Caspian coastline, with Kazakhstan having the longest coastline at 2,320 kilometers, followed by Turkmenistan at 1,700 kilometers, Iran at 720 kilometers, Azerbaijan at 450 kilometers, and Russia at 690 kilometers. All five Caspian littoral states maintain naval forces on the sea. According to a treaty signed between Iran and the Soviet Union, the sea is technically a lake and was divided into two sectors (Iranian and Soviet), but the resources (then mainly fish) were commonly shared. The line between the two sectors was considered an international border in a common lake, like Lake Albert. The Soviet sector was sub-divided into the four littoral republics' administrative sectors. Russia, Kazakhstan, and Azerbaijan have bilateral agreements with each other based on median lines. Because of their use by the three nations, median lines seem to be the most likely method of delineating territory in future agreements. However, Iran insists on a single, multilateral agreement among the five nations, aiming for a one-fifth share. Azerbaijan is at odds with Iran over some of the sea's oil fields. Occasionally, Iranian patrol boats have fired at vessels sent by Azerbaijan for exploration into the disputed region. There are similar tensions between Azerbaijan and Turkmenistan, the latter claiming that the former has pumped more oil than agreed from a field, recognized by both parties as shared. The Caspian littoral states' meeting in 2007 signed an accord that only allows ships bearing flags of littoral states to enter the sea.
The Environmental Crisis of the 21st Century
The Caspian Sea suffers from an enormous burden of pollution from oil extraction and refining, offshore oil fields, radioactive wastes from nuclear power plants, and huge volumes of untreated sewage and industrial waste introduced mainly by the Volga River. The Volga River, the longest river in Europe, drains 20% of the European land area and is the source of 80% of the Caspian's inflow. Heavy development in its lower reaches has caused numerous unregulated releases of chemical and biological pollutants. The magnitude of fossil fuel extraction and transport activity in the Caspian also poses a risk to the environment. The island of Vulf off Baku, for example, has suffered ecological damage as a result of the petrochemical industry; this has significantly decreased the number of species of marine birds in the area. Existing and planned oil and gas pipelines under the sea further increase the potential threat to the environment. The high concentration of mud volcanoes under the Caspian Sea were thought to be the cause of a fire that broke out 75 kilometers from Baku on the 5th of July 2021. The State oil company of Azerbaijan SOCAR said preliminary information indicated it was a mud volcano which spewed both mud and flammable gas. It is calculated that during the 21st century, the water level of the Caspian will decrease by 9 to 18 meters due to the acceleration of evaporation due to global warming and the process of desertification, causing an ecocide. Under medium to high emission scenarios, a decline towards the high end, of 18 meters, could mean an area of up to 100,000 square kilometers converting to land, a 37% reduction to current water area. Under such a scenario all ecologically significant areas of the Caspian Sea would experience a large reduction in sea level. On the 23rd of October 2021, Kazakhstan President Kassym-Jomart Tokayev signed the Protocol for the Protection of the Caspian Sea against Pollution from Land-based Sources in order to ensure better protection for the biodiversity of the Caspian Sea. In July 2025, the Caspian Sea reached its lowest recorded level, falling to less than 29 meters below sea level.