Discover the Largest Single Endorheic Lake in the World

Written by Michael Steinkirchner
Updated: June 3, 2023
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The Caspian Sea is the largest endorheic lake in the world.

Water is one of the most omnipresent elements of existence. It is 60% of the human body and covers 71% of Earth. Over the course of our history, human beings have been inextricably drawn to oceans, rivers, and lakes for their access to trade routes, sources of nourishment and hydration, and of course, their natural beauty. 

Lakes are no exception. We have even gone so far as to construct our own artificial lakes to generate hydroelectricity, aid in water supply, boost agricultural or industrial industries, or simply to have a beautiful place to go.

Many lakes are the product of water’s natural passage from rivers or oceans, but some lakes are endorheic, meaning there is no external or underground flow to the sea.

What and where is the world’s largest endorheic lake? 

Where And What Is The Caspian Sea?

Caspian sea

The Caspian Sea, about 600 miles in length, is bigger than any other lake, with an area of 143,000 miles and a volume of 18,800 cubic miles.

©Marina Khlybova/

The Caspian Sea is not only the world’s biggest endorheic lake but also the largest lake on Earth. It can be found along the borders of five European/Asian countries (Kazahkstan to the north and east, Turkmenistan to the east, Iran to the south, and Russia and Azerbaijan to the west). It lies cradled directly between the Caucasus Mountains and the Ural Mountains and steppes of Asia.

This precarious location makes the Caspian Sea – a wellspring of oil and natural gas – a fascinating area because it serves as an aqueous border between countries with vastly different political systems, ideologies, and ways of life. 

The deepest part of the Caspian Sea is in the south, at 3,300 feet, while its shallowest depths are found on the northern edge, only 16 to 20 feet below the surface. The Caspian Sea, which runs about 600 miles in length, is bigger than any other lake, with an area of 143,000 miles and a volume of 18,800 cubic miles. Its total surface area is around 143,244 square miles.

Although more than 130 rivers flow into the Caspian Sea, it receives 80% of its water from the Volga River in Russia. It has not always been endorheic, as it used to be connected to the Black Sea and the Mediterranean Sea. Because it does not empty out into the ocean, the Caspian Sea only diminishes in size via the process of evaporation. It is also the world’s largest endorheic saline lake.

What is an Endorheic Lake? 

Endorheic is a hydrological term that describes a water body with no outlet to the ocean. It comes from the Greek words rheîn, “flow,” and éndon, “within.”

Roughly 20% of the planet is covered in endorheic lakes. They are usually high in saline content because they only receive water from streams or rivers and only lose it through evaporation. This process leaves behind many solutes. 

Endorheic lakes are most commonly found far from the shoreline and in dry, warm climates. They should not be confused with cyrptorheic lakes, which do drain to sea but via underground water flow.

Is the Caspian Sea a Lake or a Sea?

Map of the Caspian Sea

From a historical perspective, the Caspian Sea can be thought of as a sea because it used to flow out to other bodies of water that connected with the ocean.


Despite its name, the Caspian Sea can, interestingly enough, be categorized as either a sea or a lake. While there are broad technical definitions that distinguish between seas and lakes according to things like their size, water content, and in/out flow, there are cases where a body of water can be both.

Part of the reason for this is that the definition of a lake or a sea is not universally agreed upon between nations and cultures. 

The Caspian Summit – comprised of the sea’s five bordering nations, has met 5 times so far in attempts to determine the legal status of The Caspian Sea, but to date, no significant definitions have been agreed upon. This has multiple economic and political implications because international law and the jurisdiction of The United Nations do not apply to lakes, only to seawater. 

Distinctions such as these become very important when considering the abundance of petroleum near and under The Caspian Sea. If it becomes categorized as a sea, it cannot be under the control of any single nation but instead subject to the Law of The Sea Treaty. If it is determined to be a lake, there is a possibility for its trade routes and energy resources to be monopolized by one country and excluded from others.

At one time, the only two nations that bordered the Caspian Sea were the USSR and Iran, and they agreed to classify it as a lake. This has led to modern-day Iran identifying the Caspian as a lake, while countries like Kazakhstan (which has the largest shoreline alongside it) choose to define it as a sea.

From a historical perspective, the Caspian Sea can be thought of as a sea, because it used to flow out to other bodies of water that connected with the ocean. It is only since somewhere near the halfway point of the Miocene Epoch that the Caspian Sea became closed off from the ocean, befitting the definition of a lake.

The vast expanse of the Caspian Sea, stretching as it does across the borders of many countries, also engenders thoughts of distance and travel – the kinds of imagery typically associated with seas.

However, seas are usually categorized by a strict composition of salt water. The Caspian Sea has a salinity content of only about 1.2%, which is one-third the amount of salinity found in most seawater. The enclosed nature of the present-day Caspian Sea is also partially responsible for its occasional classification as a lake. 

For What Do Its Neighboring Countries Use The Caspian Sea?

Because the Caspian Sea is the direct border alongside five different countries, cooperation and communication between these nations is a must. The Caspian is rich in oil, minerals, and natural gas, which comprise around 10% of their national GDP and 40% of their exported material. Additional areas of use include fishing, tourism, transport, trade routes, infrastructure, and even salt extraction. 

The biggest consideration, however, is oil and natural gas. Russia is second only to the United States when it comes to the production of these, and Iran has the second-largest oil reserves in the world.

Oil has been present on the shores of the Caspian Sea since at least the 10th century, and the first off-shore well was constructed in 1820. There are roughly 1.5 million barrels of oil a day being drawn from the Caspian Sea, most of which is extracted by Kazakhstan and Azerbaijan. For this reason, both countries are considerable beneficiaries of FDI (Foreign Direct Investment) in energy. The Caspian Sea also holds at least nine trillion cubic meters of gas.

In 2019, the Caspian Economic Forum was established in an effort to ease the establishment of investment projects, increase tourism, and boost the energy, trade, and transport industries. The Caspian Sea has been a reliable route for trade between European and Asian markets, as well as Chinese exports, making this forum of considerable importance to more than just the five bordering nations.

How Old is the Caspian Sea?

There are roughly 1.5 million barrels of oil a day being drawn from the Caspian Sea, most of which is extracted by Kazakhstan and Azerbaijan.


The Caspian Sea as a whole is believed to be around 30 million years old, though it was cut off from the sea about 5 million years ago. The northern section of the Caspian was formed even farther back in the Precambrian epoch, more than 500 million years ago, as parts of the Russian topography began shifting south. 

The Mangyshlak Bank, on the eastern shoreline of the Caspian Sea, came into existence along with the Hercynian mountains just around 300 million years ago. The southern section of the Caspian formed roughly 250 million years ago in the aftermath of continental plate shifts, and the Aberson Bank and its islands were formed just 25 million years ago alongside the Caucasus mountains.

The Caspian Sea used to be cryptorheic, with its water flowing into the Black Sea subterraneously via the Kuma-Manych Depression. A tectonic shift that occurred 14 million years ago eliminated this link, and that is how we ended up with the strictly endorheic body of water that the Caspian Sea is today.

Is There Wildlife In Or Around The Caspian Sea?

The Caspian Sea is rich in biodiversity, and the World Wildlife Fund classifies it as a distinct zoogeographical location because of its singular environment. There are around 2,000 species of animals in or near the Caspian Sea, and 20% of those are native to the region – such as the Horsfield’s tortoise, the Caspian salmon, the spur-thighed tortoise, and the Caspian seal (the only water-dwelling mammal in the region.)

Many birds, such as the Caspian turn or the Caspian gull, are drawn to the Caspian Sea as a refuge during their migration patterns. The Caspian is also home to the beluga sturgeon, the biggest freshwater fish in the world. The eggs of the beluga sturgeon are widely sought after in order to turn them into caviar, and most of the world’s beluga caviar originates in this part of the world. Unfortunately, overfishing, dam production, and chemical use around the Caspian Sea have led to the beluga sturgeon being at risk of extinction.

How Did The Caspian Sea Get Its Name?

There are a few hypotheses about the origins of the Caspian Sea’s name. One of the more likely theories is that it is named for the Kaspi/Caspi people who lived in the area around the 6th century BC. 

The amount of documentation concerning the Caspi people remains thin, but their existence is, at the very least confirmable thanks to accounts in Greek, Persian, and Egyptian archives. The Caspi people descended from Persia (present-day Iran), and their territory between Asia and Europe was referred to as Transcaucasia (parts of present-day Azerbaijan, Georgia, and Armenia). 

Many names have been assigned to the Caspian Sea throughout history, including the Khazar Sea, the Khvalynian Sea (ancient Russia), and the Mazandaran Sea (modern Iran). When translated to their native tongues, many of its historical names are derived from the same root. 

For example, in Kazakh (the language of Kazakhstan), the name for the Caspian Sea is “Kaspiy tenizi.” In Russian, it translates to “Kaspiyskyoye More,” and in Kyrgyz (Kirghizistan’s national language), it is referred to as “Kaspiy denizi.” 

Another credible theory is that the Caspian Sea owes its name to the Iranian city of Qazvin, just 93 miles northwest of Tehran. Today it is famous as the center of Iranian calligraphy, but in pre-modern times the Caspian Sea was referred to as “Bar Qazvin,” which means “Sea of Qazvin.” Words tend to change with time, and many historians and linguists believe the term eventually mutated from Qazvin to Caspian as new cultures and regimes took root. 

Where is the Caspian Sea Located on a Map?

The capital of Azerbaijan is situated on the Absheron Peninsula that juts out into the Caspian Sea. This city, Baku, has a population of about two million people and lies in a temperate semi-arid climate that is generally pleasant and healthy (it used to be a Soviet vacation spot), but it is very windy.

The photo featured at the top of this post is ©

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