Caspian Sea
The Caspian Sea holds a record that no ocean can claim: it is the largest inland body of water on Earth. Bigger than Japan by surface area, it sits in a geographic no-man's-land between Europe and Asia, east of the Caucasus and north of the Iranian Plateau. Five nations share its shores today: Kazakhstan, Russia, Azerbaijan, Iran, and Turkmenistan. Each has a different name for it, different claims over its waters, and different stakes in what lies beneath. But the Caspian refuses easy classification. Call it a lake and certain treaties apply. Call it a sea and entirely different rules govern it. Lawyers, heads of state, and ecologists have spent decades arguing which it is. Meanwhile, the water itself keeps falling. In July 2025, the Caspian reached its lowest recorded level. The questions this documentary will answer: how did a body of water this vast come to exist in the middle of a continent, what lives inside it, what has it powered throughout human history, and what is being lost?
Roughly 30 million years ago, the Caspian's southern basin formed as a remnant of the ancient Paratethys Sea. The seafloor there is oceanic basalt, not the continental granite you find under most lakes. That fact alone marks the Caspian as something unusual: a landlocked body of water with an oceanic pedigree. Tectonic uplift and falling sea levels sealed it off in the Late Miocene, about 5.5 million years ago. During the Pliocene it was comparatively small, but its surface area increased roughly fivefold near the Pliocene-Pleistocene transition. Warm, dry periods nearly dried it out entirely, leaving behind thick evaporite deposits of halite. Cool, wet periods flooded it back to life.
The Arabian Peninsula's collision with West Asia pushed up the Kopet Dag and Caucasus Mountains, which set the southern and western limits of the basin. The Caspian was periodically connected to the Black Sea and Aral Sea through geological history, and during the Akchagylian period it expanded to more than three times its present size, reconnecting briefly with both neighboring seas. The salinity pattern the Caspian has today, nearly fresh in the north, increasingly brackish toward the Iranian south, directly reflects its geological and hydrological inheritance: the Volga pours fresh water into the shallow northern end, while the south receives almost no riverine flow and sits closer to oceanic conditions.
Strabo, who died around the year AD 24, wrote that the Caspii tribe once inhabited the territory southwest of the sea and gave both the land and the water their name, noting that the tribe had since disappeared. That single ancient observation underpins a name used across dozens of modern languages. Medieval Arabic sources called it Bahr al-Khazar, the sea of the Khazars, after the powerful empire based north of the sea between the 7th and 10th centuries. Modern Arabic shifted to Bahr Qazvin, an Arabized echo of the Persian city Qazvin, which shares the same root as Caspi.
Iran has long called it the Mazandaran Sea, after the historic province on its southern shore. Old Russian sources used Khvalyn or Khvalis Sea, derived from the name of Khwarezmia. Classical Greek and Persian writers knew it as the Hyrcanian Sea. Renaissance cartographers gave it different labels on different maps: Oronce Fine's 1531 world map named it the Abbacuch Sea, the Mercator 1569 map called it the Mar de Sala, and Ortelius's 1570 map used Mar de Bachu. The Kumyk people called it the Kumyk Sea or Tarki Sea, after their historical capital Tarki. No other body of water on Earth carries quite so many geographically distinct proper names, each one a window into a different civilization's sphere of influence.
The Caspian seal, Pusa caspica, is the only aquatic mammal that evolved entirely within the sea. A century ago more than one million lived there. Fewer than 10 percent of that population remains today. The seal shares the water with six native sturgeon species, including the beluga, which is arguably the largest freshwater fish in the world and can grow to 430 centimeters. The beluga sturgeon also produces roe that becomes caviar, priced at more than 1,500 Azerbaijani manats per kilogram, equivalent to around US$880. That price is high enough that fishermen have historically been able to afford bribes to ensure regulators look the other way, making anti-poaching rules largely ineffective in practice.
The basin as a whole contains 160 native fish species and subspecies across more than 60 genera, and about 62 percent of those are found nowhere else on Earth. The goby family alone accounts for 35 species and subspecies in the lake proper. The genus Alosa contains 18 endemic species or subspecies; Benthophilus holds 16. Rock art at Gobustan, in Azerbaijan, may depict oceanic animals including what researchers have interpreted as beaked whales or dolphins, though some scholars think a large carving on Kichikdash Mountain more likely represents the beluga sturgeon given its depicted size. The Caspian turtle is a wholly freshwater species, while the zebra mussel, native here, has become an invasive species in waterways far beyond its home range. In the Samur River delta, over a thousand plant species grow, including temperate broadleaf and tropical liana forests that date to the Tertiary period. The Samursky National Park was created in 2018 to protect much of that delta.
Oil wells were drilled near the Caspian as early as the 10th century, when the resource was extracted for medicinal use, heating, and lighting. By the 16th century, English traders Thomas Bannister and Jeffrey Duckett described the area around Baku as containing a marvelous quantity of oil issuing from the ground, noting both a black variety called nefte and a white, precious variety they equated with petroleum. That observation was written down centuries before any commercial oil industry existed anywhere in the world.
Serious industrial development came in 1873, when exploration began on the Absheron Peninsula near the villages of Balakhanli, Sabunchi, Ramana, and Bibi Heybat, where total recoverable reserves were estimated at more than 500 million tons. By 1900, Baku held more than 3,000 oil wells, 2,000 of which were producing at industrial scale. By the end of the 19th century the city was known internationally as the black gold capital. In 1941, Azerbaijan's Baku region alone produced a record 23.5 million tons of oil per year, nearly 72 percent of the Soviet Union's total output.
After the Soviet collapse, the 1994 Contract of the Century opened Baku's fields to international development. The Baku-Tbilisi-Ceyhan pipeline, which carries Azeri oil to the Turkish Mediterranean port of Ceyhan, opened in 2006. As of 2001, the broader Caspian region produced 1.4 to 1.5 million barrels per day, about 1.9 percent of world output, with Kazakhstan accounting for 55 percent and Azerbaijan about 20 percent of that regional total. In 1998, Dick Cheney remarked that he could not think of another region that had emerged so suddenly to become so strategically significant.
The Caspian's water level has never been stable. Between 1929 and 1977, the sea fell measurably; then from 1977 to 1995 it rose again. Since 1995 the oscillations have been smaller, but projections now point toward a dramatic long-term decline. Climate models suggest water levels could drop by as much as 21 meters by 2100. In July 2025, the sea reached its lowest recorded level, falling to less than a threshold that scientists described as a crisis point. A 37 percent reduction in water area is possible under high-emission scenarios, and under those conditions every ecologically significant zone in the Caspian would experience severe loss.
The United Nations Environment Programme has described the sea as suffering an enormous burden of pollution from oil extraction, offshore drilling, radioactive wastes from nuclear power plants, and vast volumes of untreated sewage and industrial waste introduced mainly through the Volga. The island of Vulf, off Baku, has seen a significant decline in marine bird species as a direct result of the petrochemical industry. Mud volcanoes on the seafloor ignited a fire 75 kilometers from Baku on the 5th of July 2021, with Azerbaijan's state oil company SOCAR concluding that a mud volcano likely triggered the blaze. A leaked U.S. diplomatic cable revealed that BP covered up a gas leak and blowout incident in September 2008 in the Azeri-Chirag-Guneshi field. Kazakhstan's President Kassym-Jomart Tokayev signed the Protocol for the Protection of the Caspian Sea against Pollution from Land-based Sources on the 23rd of October 2021, a concrete but belated step toward governance.
A 1931 treaty between Iran and the Soviet Union declared the sea the common property of both nations and divided it into two sectors. When the Soviet Union collapsed, that bilateral arrangement became a five-way problem almost overnight. By 2000, negotiations over the sea's legal status had run for nearly a decade without resolution. The stakes were enormous: whether the Caspian was legally a sea or a lake determined which international treaties applied, how oil and gas under the seabed could be divided, who had fishing rights where, and whether foreign vessels had the right to sail its waters through Russia's inland canal connections to the Black Sea and Baltic.
Russia, Kazakhstan, and Azerbaijan reached bilateral median-line agreements among themselves, but Iran pushed consistently for a single multilateral deal that would give each of the five states a one-fifth share. Iranian patrol boats have at times fired at Azerbaijani exploration vessels operating in disputed zones. There have been similar tensions between Azerbaijan and Turkmenistan over allegations that Azerbaijan pumped more oil than agreed from a jointly recognized shared field.
The breakthrough came at the fifth Caspian Summit, held on the 12th of August 2018 in the Kazakh port city of Aktau. The five leaders signed the Convention on the Legal Status of the Caspian Sea. The convention grants each state jurisdiction over 15 nautical miles of territorial waters and an additional 10 nautical miles of exclusive fishing rights, while declaring the remainder international waters. The seabed was left deliberately undefined, subject to future bilateral agreements. The convention does not address environmental protection at all. That gap leaves the Caspian's ecological future in the hands of the same states whose resource extraction has already driven the Caspian seal population to fewer than 10 percent of its historical peak.
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Common questions
Why is the Caspian Sea called a sea if it is landlocked?
The Caspian is called a sea largely because of its size and its oceanic origins. Its southern basin is a remnant of the ancient Paratethys Sea, and its seafloor is oceanic basalt rather than continental rock. The legal question of whether it is a sea or a lake remained unresolved in international law until the 2018 Aktau Convention, which declared it legally neither.
How salty is the Caspian Sea?
The Caspian has a salinity of approximately 1.2 percent, about one third the salinity of average ocean water. This classifies it as a brackish body of water. Salinity varies significantly: the north is nearly fresh due to Volga River inflow, while the south, near Iran, is most saline because little riverine flow reaches it there.
What is happening to the Caspian Sea's water level?
The water level has fluctuated throughout history, falling from 1929 to 1977 and then rising until 1995. Since then smaller oscillations have continued. Climate projections now suggest the level could fall by as much as 21 meters by 2100 due to accelerating evaporation and desertification. In July 2025 the sea reached its lowest recorded level.
Why is Caspian caviar so expensive and endangered?
Caspian caviar comes from six native sturgeon species whose populations have been severely depleted by overfishing. Caviar specifically targets reproductive females, compounding the damage to the population. The high price, over US$880 per kilogram as of recent figures, means fishermen can afford to bribe regulators, making protective rules largely ineffective in many areas.
How many countries share the Caspian coastline?
Five countries border the Caspian: Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the southwest, Iran to the south, and Turkmenistan to the southeast. Their coastlines collectively extend across a substantial stretch of the sea's perimeter.
What is the Caspian's connection to oil production history?
Oil was extracted near the Caspian as early as the 10th century. By 1900, Baku had more than 3,000 oil wells. By 1941, the Baku region alone produced nearly 72 percent of the Soviet Union's total oil output. In 1994, the Contract of the Century opened the fields to international investment, and the Baku-Tbilisi-Ceyhan pipeline to Turkey opened in 2006.