Caspian Sea: The Largest Lake in the World

The Caspian Sea is, by standard definition, the largest lake on Earth. It is the largest enclosed inland body of water, and thus sometimes referred to as a sea.

Caspian Sea Stats

Lake NameCaspian Sea
Surface area377001.910
Maximum depth1025.0
Average depth200.5
Lake typeEndorheic, saline
Catchment area1404108.00
InflowsVolga River, Ural River, Kura River, Terek River, Sulak River
Shore length15829.37
Age2 - 20 million years
SettlementsBaku (Azerbaijan), Rasht (Iran), Aktau (Kazakhstan), Makhachkala (Russia), Türkmenbaşy (Turkmenistan)
Residence time107883.0
Average discharge8110.642

Caspian Sea Accommodation


Caspian Sea’s surface area is 378,000 km2 or 143,200 sq mi, and it boasts a volume of 78,200 km3. The lake is endorheic (meaning it has no outflows), and sits at the border between Europe and Asia. The countries on its shores are Kazakhstan to the NE, Russia to the NW, Azerbaijan to the West, Iran to the South and Turkmenistan to the SE. The Caucasus Mountains are located West of the Caspian Sea, while the vast steppes of Central Asia are located to the East. The Caspian Depression in the lake’s northern section is one of the lowest points on Earth.

Throughout history, the lake has been considered a sea or an ocean, because of its saltiness and size. Its salinity is actually about one third of most seawater, at about 1.2%, or 12 g/l. However, several of the Caspian Sea’s characteristics classify it as a lake, rather than a sea. Firstly, it’s not either directly or indirectly connected to an ocean basin. Secondly, it’s located at an altitude of 22 meters below the sea level, while all the other seas and oceans are located roughly at the same altitude, known as altitude 0 or sea level.

Regarding its size, several numbers have been acknowledged in different stages, depending on the measurements’ accuracy, whether certain lagoons such as Garabogazköl Aylagy were included or not, and so on. In 1930, its surface area was estimated at about 424,300 km2, in 1952 at 393,200 km2, and in 1957 at 371,000 km2.

Named After an Ancient Tribe

The word "Caspian" is derived from Caspi, an ancient tribe that lived in the southwestern part of the sea, in Transcaucasia. There is also a region in the Iranian Tehran province called Caspian Gates, which suggests that the tribe moved to the South of sea at one point.

Many Different Names

The lake was and still is known under many different names. The Greeks and Persians used to call the lake the the Hyrcanian Ocean. In Persian antiquity but also in modern Iran, the Caspian Sea is known as the Mazandaran Sea. Indians used to call it Kashyap Sagar, which in Turkey is known under the name of Khazar Sea.

Russian people used to call it Khvalyn or Khvalis Sea, derived from the name of Khwarezmia, while ancient Arabic sources know it under the name of Baḥr Gīlān, which means "the Gilan Sea".

Formed from the Ancient Paratethys Sea

The Caspian Sea is a remnant of the ancient Paratethys Sea, like the Black Sea, the Aral Sea, Lake Urmia and Lake Oroumieh. A tectonic uplift and a fall in sea level caused it to became landlocked approximately 5.5 million years ago. The sea almost dried up during warm and dry periods.

In its northern section where the Volga River drains into the Caspian Sea, it is a freshwater lake. However, the Iranian shore is more saline, as there is little flow coming from its catchment basin. The Garabogazköl embayment dried up during the 1980s because the main water flow coming from the main body of the Caspian Sea was blocked. It has been restored, and here salinity exceeds that of the oceans’ by a factor of 10.

About 40% of All Lake Water in the World

As the largest lake in the world (similar in size to California), the Caspian Sea accounts for approximately 40 - 44% of the Earth’s total lake water volume. The lake is divided into 3 regions: the Northern Caspian, the Middle Caspian and the Southern Caspian. The Northern and the Middle Caspian are separated by the Mangyshlak Threshold, which runs through Cape Tiub-Karagan and Chechen Island. The Middle and Southern Caspian are separated by the Apsheron Threshold, which runs through Cape Kuuli and Zhiloi Island.

The Eastern inlet of the Caspian Sea (in Turkmenistan) is called Garabogazköl Bay and is sometimes considered a distinct lake because it’s cut off from the Caspian Sea by an isthmus.

Three very Different Lake Sections

The Northern section is very shallow and only accounts for about 1% of the total water volume, but accounts for 25% of the surface area. It has an average depth of 5-6 meters (about 20 ft) and it usually freezes in winter. Then, the lake floor plunges towards the Middle Caspian to an average depth of 190 meters, or 620 ft. The Middle Caspian accounts for 33% of the total water volume. Finally, the Southern Caspian boasts the greatest depths, of more than 1,000 meters (3,300 ft), and accounts for 66% of the total water volume. The Middle and the Southern Caspian sections both account for approximately 37% of the surface area each.

Its shores are extremely varied. It reaches greater heights in the South, when it comes in contact with the Alborz (or Elburz) mountain range and to the Caucasus mountains to the West. However, it’s low and features plains and deltas at the mouths of the Kura River and Volga River. The lake’s maximum width is 435 kilometers, but it also narrows to about 200 kilometers.

Volga, the Caspian Sea's Great Tributary

The Volga River, at 3,692 km (2,294 mi) the longest river in Europe, is Caspian Sea’s most important tributary among the 130. Other notable affluents include the Ural River (2,428 km or 1,509 miles), Kura River (1,515 km or 941 miles), Terek River (623 km or 387 miles), and Sulak River (144 km). These 5 rivers contribute with approximately 90% of the lake’s freshwater supply, more specifically: Volga with 241 km3, Kura with 13 km3, Terek with 8.5 km3, Ural with 8.1 km3, and Sulak with 4 km3. The Volga River Delta, located in the Prikaspiisk lowlands, covers approximately 10,000 km2 and is 200 kilometers in width.

Amu Darya and Syr Darya both used to change courses in the past to drain into the Caspian Sea.

The lake has several small islands with a total area of approximately 2,000 km2 (or 770 sq mi), which are mainly located in the Northern Caspian. Noteworthy here is the Tyuleniy Archipelago, which is an Important Bird Area (IBA).  However its the largest island, Ogurja Ada, is located in the Southern Caspian. It is 37 km (23 miles) long, and gazelles roam freely on the island. Other islands include Chechen, Tyuleny, Morskoy, Kulaly, Zhiloy, and Ogurchin.

Kara-Bogaz Gol: the Largest Lagoon in the World

The Kara-Bogaz Gol is located on the lake’s eastern coast. With a surface area of 18,000 km2, it can easily be considered the largest lagoon in the world. It is separated from the Caspian Sea by sand bars.

In 1980, a dam was built between the Caspian Sea and Kara-Bogaz Gol, in order to prevent water outflow from the Caspian Sea to the lagoon and a subsequent drop in water level. The dam was effective, so effective in fact that more than 40 km3 were retained in the Caspian Sea, which led to an increase of 11 cm in its water level. A spillway was created in 1984 to allow some water discharge, and in June 1992, the dam was removed completely.

Great Biodiversity

The Caspian Depression is located adjacent to the North Caspian Shore and lies 27 meters (89 feet) below sea level. The Caucasus mountains are situated near the lake’s western shore, while the Asian steppes stretch from the northeastern shore. Cold, continental desert climates characterize the northern and eastern shores, while the southern and southwestern shore are warm due to a mix of mountain ranges and highlands. The drastic climate variations resulted in great biodiversity.


As already mentioned, the Caspian Sea can be considered both a sea and a lake. Although it is not a freshwater lake, it is widely considered to be the world’s largest lake, with 3.5 more water than all of the Great Lakes combined.

The Volga River contributes with about 80% of the Caspian Sea’s inflow, but the lake doesn’t have a natural outflow. All this means that the Caspian Sea’s ecosystem is a closed basin, independent of the ocean’s basin.

Water level in the lake has fluctuated throughout history. Russian historians claim that a rising of the lake’s level (possibly caused by Amu Darya changing its course to the Caspian Sea), has caused floods in coastal towns between the 13th and the 16th centuries.

An even more interesting fact is that the Caspian Sea levels are dependent on atmospheric conditions in the North Atlantic Ocean, thousands of miles to the northwest. This is because the discharge of the Volga, its main inflow, depends on rainfall levels from its catchment basin, which in turn are affected by the cycles of the North Atlantic Oscillation.

The latest changes in the lake’s level were a 3-meter fall (about 10 ft), that happened between 1929 and 1977, which was followed by a 3-meter rise that took place between 1977 and 1995.

Environmental Concerns

The Volga River, the Caspian Sea’s most important inflow, is also a major source of chemical and biological pollutants. Fossil fuel extraction operations taking place in the region are also a major risk to the lake’s water quality. Furthermore, several underwater oil and gas pipelines have been proposed or constructed. The petrochemical industry has affected the island of Vulf in Azerbaijan, causing a significant decrease in the number of species of birds in the area.


Since the Caspian Sea is a lake of superlatives, it’s no wonder that the largest freshwater fish in the world can also be found here. We are talking about the beluga sturgeon, a fish that is also known for its eggs that are processed into caviar.

Unfortunately, overfishing is a problem and it has depleted many historic fisheries, to the point of economic exhaustion of tuna fisheries. Sturgeon populations are also severely threatened, and many environmentalists believe that sturgeon fishing should be banned completely until populations recover. However, high demand and price of caviar make regulations ineffective. Even more, since reproductive females are targeted for caviar harvesting, this further endangers fish stocks.

Many Endemic Species

Several species of animals are named after the region, like the Caspian gull, the Caspian tern, and the Caspian seal, which is the only aquatic mammal that can be found here and is endemic to the lake.

There are 115 species of fish found in the lake. Some of the species of fish that are endemic to the lake include the kutum (or the Caspian white fish), Caspian roach, Caspian marine shad, Caspian bream, and the Caspian salmon. The Caspian salmon is a subspecies of trout and is critically endangered.

The spur-thighed tortoise and Horsfield’s tortoise are two of the most important aquatic reptiles that are native to the Caspian Sea. Caspian turtles can also be found in nearby waters. The Caspian Sea also shares 2 species with the Black Sea: the zebra mussel and the common carp.

Coastal wetlands are an ideal habitat for various bird species. Birds are present throughout the year all around the lake, a delight for visitors who can experience the beauty of protected ecological resources.

The Gobustan petroglyphs might also suggest that dolphins and porpoises once lived in the Caspian sea. The rock art on Kichikdash Mountain is assumed to represent a dolphin, but it could also represent a beluga sturgeon.


As well as in the case of fauna, there are also many endemic and rare plant species around the lake, especially in the Volga delta. Plants which are adapted to the loose sands of the Central Asian Deserts can also be found along the shores of the lake.

There are however a few important factors that lead to a limitation in the number of plant species. These factors include water pollution, land reclamation activities, and water level changes in the Caspian sea. Approximately 11 plant species can be found in the delta of the Samur River, including liana forests.


Various caves in Georgia and Azerbaijan (like Kudaro and Azykh) suggest human occupation in the region, and there is evidence of human occupation in the Lower Palaeolithic in the Ganj Par and Darband Cave sites. Neanderthal remains have also been discovered in a cave in Georgia. Other discoveries point to human habitation in the area as far back as 11,000 years ago.

The area has always been known as a region rich in energy resource. Wells have been dug in the region starting with the 10th century. The rich oil and gas deposits have attracted the interest of Europeans as early as the 16th century.

The Caspian Sea was first charted by the pioneering explorer Fedor I. Soimonov in the 18th century. He drew the first modern maps of the lake which were published in 1720 by the Russian Academy of Sciences.

More recently, in 1950, construction of the Main Turkmen Canal started, ordered by Joseph Stalin. The canal would have been used for shipping and was meant to run from Nukus (on the  Amu Darya) to Krasnovodsk (on the Caspian Sea). However, the canal’s construction was abandoned.

A Region Rich in Oil

The lake is the site of the world’s first offshore wells, which were built in the Bibi-Heybat Bay, near Azerbaijan’s current capital, Baku. Some of the largest oil fields known to exist at that time started being exploited in 1873, on the Absheron peninsula. By 1900, Baku was known as the "black gold capital", with more than 3,000 wells.

Needless to say, in the early 20th century, Baku was the center of the oil industry. The republic’s oil industry came under the control of the Soviet Union in 1920, when Azerbaijan was captured by the Bolsheviks. 23.5 million tons of oil were being produced in Azerbaijan in 1941.

The  "Contract of the Century" was signed in 1994, which signaled the start of international development of the Baku oil fields. The Baku–Tbilisi–Ceyhan pipeline was opened in 2006, which allows Azerbaijan oil to reach the Turkish Mediterranean port of Ceyhan directly.

Due to its large oil and gas reserves, the Caspian Sea is a major economic importance. Oil reserves in the region are estimated to be between 18 and 35 billion barrels. Comparatively, they are similar in size and even exceed reserves in the North Sea (17 billion) and in the United States (22 billion). Natural gas reserves amount to even more than oil reserves.

Territorial Disputes

The importance of the region has been noted by many, and negotiations regarding territories in the Caspian Sea have been taking place for nearly 10 years among the 5 states on the lake’s shores. The lake boasts important mineral resources like oil and gas and many fisheries.

Access to international waters through Russia’s Volga River is another important issue, and is of great importance to the 3 landlocked countries of Azerbaijan, Turkmenistan and Kazakhstan.


The Caspian Sea itself is endorheic, but it does have an important tributary, the Volga. This major Russian river is connected to the Don River through shipping canals, which also gives it access to the Black Sea. It’s also connected to the Baltic Sea, with canals to Northern Dvina and the White Sea. The Kuma River is connected to the Don basin also.

There are several ferries operating on the sea, including lines between TürkmenbaÅŸy in Turkmenistan and Baku, between Baku and Aktau and between cities in Iran and Russia. Most ferries are used for cargo shipping, but the Baku - TürkmenbaÅŸy and the Baku - Aktau accept passengers as well.


The importance of the Caspian Sea is undeniable. Economically, its oil and gas reserves have always held a strong allure. Its caviar is appreciated by many around the world. Finally, its rich biological diversity has always attracted scientists and nature lovers. It’s up to us to make sure that the lake recovers from the strains it's been put through.

Caspian Sea Map