The Caspian Sea is the world's largest inland
body of water, often described as the
world's largest lake or a full-fledged sea. An
endorheic basin, it lies between Europe and Asia; east of the
Caucasus
The Caucasus () or Caucasia (), is a region between the Black Sea and the Caspian Sea, mainly comprising Armenia, Azerbaijan, Georgia (country), Georgia, and parts of Southern Russia. The Caucasus Mountains, including the Greater Caucasus range ...
, west of the broad
of
Central Asia
Central Asia, also known as Middle Asia, is a region of Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the c ...

, south of the fertile plains of
Southern Russia in
, and north of the mountainous
of
. It covers a surface area of (excluding the highly saline lagoon of
Garabogazköl to its east) and a volume of . It has a
of approximately 1.2% (12 g/L), about a third of the salinity of average
. It is bounded by
to the northeast,
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

to the northwest,
to the southwest,
Iran
Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

to the south, and
to the southeast.
The sea stretches nearly from north to south, with an average width of . Its gross coverage is and the surface is about below
sea level
Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

. Its main freshwater
inflow, Europe's longest river, the
, enters at the shallow north end. Two deep basins form its central and southern zones. These lead to horizontal differences in temperature, salinity, and ecology. The
in the south reaches below sea level, which is the second-lowest natural non-oceanic
depression on Earth after
(). Written accounts from the ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its salinity and large size.
The Caspian Sea is home to a wide range of species and is known for its
and oil industries. Pollution from the oil industry and dams on rivers draining into it have harmed its ecology.
Etymology
The lake's name stems from
Caspi, an ancient people who lived to the southwest of the sea in
Transcaucasia.
Strabo
Strabo''Strabo'' (meaning "squinty", as in strabismus) was a term employed by the Romans for anyone whose eyes were distorted or deformed. The father of Pompey was called "Pompeius Strabo". A native of Sicily so clear-sighted that he could see ...

(died circa AD 24) wrote that "to the country of the Albanians (
not to be confused with the country of
Albania
Albania ( ; sq, Shqipëri or ), or , also or . officially the Republic of Albania ( sq, Republika e Shqipërisë), is a country in Southeast Europe, Southeastern Europe. It is located on the Adriatic Sea, Adriatic and Ionian Seas within the ...

) belongs also the territory called Caspiane, which was named after the Caspian tribe, as was also the sea; but the tribe has now disappeared". Moreover, the
Caspian Gates, part of
Iran
Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

's
Tehran province, may evince such a people migrated to the south. The Iranian city of
shares the root of its name with this common name for the sea. The traditional and medieval Arabic name for the sea was Bahr(sea) Xazar but in recent centuries common and standard name in Arabic language is Baḥr
Arabized from Caspian. In modern russian: Каспи́йское мо́ре, ''Kaspiyskoye more''.
[''Iran'' (5th ed., 2008), by Andrew Burke and Mark Elliott]
p. 28
, Lonely Planet Publications,
Some Turkic ethnic groups refer to it with the Caspi(an) descriptor; in
Kazakh it is called , ''Kaspiy teñizi'', ky, Каспий деңизи, Kaspiy deñizi, uz, Kaspiy dengizi. Others refer to it as the ''Khazar sea'': tk, Hazar deňizi; az, Xəzər dənizi, tr, Hazar denizi. In all these the first word refers to the historical
who had a large empire based to the north of the Caspian Sea between the 7th and 10th centuries.
In Iran, the lake is referred to as the ''Mazandaran Sea'' ( fa, دریای مازندران), after the historic
at its southern shores.
Old Russian sources use the ''Khvalyn'' or ''Khvalis'' Sea () after the name of
Khwarezmia.
Among Greeks and Persians in
classical antiquity
Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ...
it was the
Hyrcanian ocean.
Renaissance European maps labelled it as the ''Abbacuch Sea'' (Oronce Fine's 1531 world map), ''Mar de
'' (Ortellius' 1570 map), or ''Mar de Sala'' (Mercator's 1569 map).
It was also sometimes called the Kumyk Sea and Tarki Sea (derived from the name of the
and their historical capital
).
Basin countries
Border countries
*
*
Iran
Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

*
*
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

*
Non-border countries
*
Armenia
Armenia (), , group=pron officially the Republic of Armenia,, is a landlocked country in the Armenian Highlands of Western Asia.The UNbr>classification of world regions places Armenia in Western Asia; the CIA World Factbook , , and '' ...

(entirety)
*
Georgia (its east part)
*
Turkey
Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with a East Thrace, small portion on th ...

(extreme north-eastern parts)
*
(extreme western parts)
Physical characteristics
Formation
The Caspian Sea, like the
, is a remnant of the ancient
Paratethys Sea. Its seafloor is, therefore, a standard oceanic
and not a continental
body. It became landlocked in the
Late Miocene
The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...
, about 5.5 million years ago, due to
tectonic uplift and a fall in
sea level
Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

. The Caspian Sea was a comparatively small endorheic lake during the
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.333 million to 2.58 , but its surface area increased 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
that were covered by wind-blown deposits and were sealed off as an
evaporite sink
A sink is a bowl-shaped plumbing fixture for washing hands, dishwashing, and other purposes. Sinks have Tap (valve), a tap (faucet) that supply hot and cold water and may include a spray feature to be used for faster rinsing. They also include ...
when cool, wet climates refilled the basin. (Comparable evaporite beds underlie the
Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...
.) Due to the current inflow of fresh water in the north, the Caspian Sea water is almost fresh in its northern portions, getting more
brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuary ...
toward the south. It is most saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is one third that of Earth's oceans. The
Garabogazköl embayment
A bay is a recessed, coast
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline ...
, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10.
Geography
The Caspian Sea is the largest inland body of water in the world by area and accounts for 40 to 44% of the total
lacustrine
A lake is an area filled with water, localized in a Depression (geology), basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the World Ocean, oce ...
waters of the world,
and covers an area larger than
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated between ...
. The coastlines of the Caspian are shared by
, Iran,
, Russia, and
. The Caspian is divided into three distinct physical regions: the Northern, Middle, and Southern Caspian.
The Northern–Middle boundary is the
Mangyshlak Threshold, which runs through
Chechen Island and Cape Tiub-Karagan. The Middle–Southern boundary is the
Apsheron Threshold, a
sill of tectonic origin between the Eurasian continent and an oceanic remnant, that runs through Zhiloi Island and Cape Kuuli.
The
Garabogazköl Bay is the saline eastern inlet of the Caspian, which is part of Turkmenistan and at times has been a lake in its own right due to the isthmus that cuts it off from the Caspian.
Differences between the three regions are dramatic. The Northern Caspian only includes the Caspian shelf,
and is very shallow; it accounts for less than 1% of the total water volume with an average depth of only . The sea noticeably drops off towards the Middle Caspian, where the average depth is .
The Southern Caspian is the deepest, with oceanic depths of over , greatly exceeding the depth of other regional seas, such as the
Persian Gulf
The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
. The Middle and Southern Caspian account for 33% and 66% of the total water volume, respectively.
The northern portion of the Caspian Sea typically freezes in the winter, and in the coldest winters ice forms in the south as well.
Over 130 rivers provide inflow to the Caspian, the
Volga River
The Volga (; russian: Во́лга, a=Ru-Волга.ogg, p=ˈvoɫɡə) is the List of rivers of Europe#Rivers of Europe by length, longest river in Europe. Situated in Russia, it flows through Central Russia to Southern Russia and into the Cas ...
being the largest. A second affluent, the
Ural River
The Ural (russian: Урал, ), known before 1775 as Yaik (russian: Яик, ba, Яйыҡ, translit=Yayıq, ; kk, Жайық, translit=Jaiyq, ), is a river flowing through Russia and Kazakhstan in the continental border between Europe and Asia ...
, flows in from the north, and the
Kura River from the west. In the past, the
Amu Darya
The Amu Darya, tk, Amyderýa/ uz, Amudaryo// tg, Амударё, Amudaryo ps, , tr, Ceyhun / Amu Derya grc, Ὦξος, Ôxos (also called the Amu, Amo River and historically known by its Latin
Latin (, or , ) is a classical language b ...
(Oxus) of Central Asia in the east often changed course to empty into the Caspian through a now-desiccated riverbed called the
Uzboy River
The Uzboy (sometimes rendered Uzboj) was a distributary
A distributary, or a distributary channel, is a stream
A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank ...
, as did the
Syr Darya
The Syr Darya (, ),, , ; rus, Сырдарья́, Syrdarjja, p=sɨrdɐˈrʲja; fa, سيردريا, Sirdaryâ; tg, Сирдарё, Sirdaryo; tr, Seyhun, Siri Derya; ar, سيحون, Seyḥūn; uz, Sirdaryo, script-Latn/. historically known ...
farther north. The Caspian has several small islands, primarily located in the north with a collective land area of roughly . Adjacent to the North Caspian is the
Caspian Depression, a low-lying region below
sea level
Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

. The
Central Asia
Central Asia, also known as Middle Asia, is a region of Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the c ...

n
s stretch across the northeast coast, while the
Caucasus mountains
The Caucasus Mountains,
: pronounced
* hy, Կովկասյան լեռներ,
: pronounced
* az, Qafqaz dağları, pronounced
* rus, Кавка́зские го́ры, Kavkázskiye góry, kɐfˈkasːkʲɪje ˈɡorɨ
* tr, Kafkas Dağla ...
hug the western shore. The
biomes
A biome () is a biogeographical unit consisting of a biological community
A community is a social unit (a group of living things) with commonality such as place, norms, religion
Religion is usually defined as a social- cultural syst ...
to both the north and east are characterized by cold, continental deserts. Conversely, the climate to the southwest and south are generally warm with uneven elevation due to a mix of highlands and
mountain range
A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...
s; the drastic changes in climate alongside the Caspian have led to a great deal of
biodiversity
Biodiversity or biological diversity is the variety and variability of life, life on Earth. Biodiversity is a measure of variation at the Genetics, genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem d ...
in the region.
The Caspian Sea has numerous islands near the coasts, but none in the deeper parts of the sea.
Ogurja Ada is the largest island. The island is long, with
gazelle
A gazelle is one of many antelope species in the genus ''Gazella'' . This article also deals with the seven species included in two further genera, ''Eudorcas'' and ''Nanger'', which were formerly considered subgenera of ''Gazella''. A third f ...
s roaming freely on it. In the North Caspian, the majority of the islands are small and uninhabited, like the
Tyuleniy Archipelago, an
Important Bird Area
An Important Bird and Biodiversity Area (IBA) is an area identified using an internationally agreed set of criteria as being globally important for the conservation of birds, bird populations.
IBA was developed and sites are identified by BirdLi ...
(IBA).
Climate
The climate of the Caspian Sea is variable, with the
cold desert climate (BWk),
cold semi-arid climate
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below Evapotranspiration#Potential evapotranspiration, potential evapotranspiration, but not as low as a des ...
(BSk), and
humid continental climate
A humid continental climate is a climate, climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by four distinct seasons and large seasonal temperature differences, with warm to hot (and often humid) summers and ...
(Dsa, Dfa) being present in the northern portions of the Caspian Sea, while the
Mediterranean climate
A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...
(Csa) and
humid subtropical climate
A humid subtropical climate is a zone of climate characterized by hot and humid summers, and cool to mild winters. These climates normally lie on the southeast side of all continents (except Antarctica), generally between latitudes 25° and 40° ...
(Cfa) are present in the southern portions of the Caspian Sea.
Hydrology

The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which ...
: the 1.2% salinity classes it with
brackish water
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuary ...
bodies.
It contains about 3.5 times as much water, by volume, as all five of North America's
Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...
combined. The
Volga River
The Volga (; russian: Во́лга, a=Ru-Волга.ogg, p=ˈvoɫɡə) is the List of rivers of Europe#Rivers of Europe by length, longest river in Europe. Situated in Russia, it flows through Central Russia to Southern Russia and into the Cas ...
(about 80% of the inflow) and the
Ural River
The Ural (russian: Урал, ), known before 1775 as Yaik (russian: Яик, ba, Яйыҡ, translit=Yayıq, ; kk, Жайық, translit=Jaiyq, ), is a river flowing through Russia and Kazakhstan in the continental border between Europe and Asia ...
discharge into the Caspian Sea, but it has no natural outflow other than by
evaporation
Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when h ...
. Thus the Caspian
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
is a
closed basin, with its own sea level history that is independent of the
eustatic level of the world's oceans.
The sea level of the Caspian has fallen and risen, often rapidly, many times over the centuries. Some Russian historians claim that a
medieval
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
rising of the Caspian, perhaps caused by the
Amu Darya
The Amu Darya, tk, Amyderýa/ uz, Amudaryo// tg, Амударё, Amudaryo ps, , tr, Ceyhun / Amu Derya grc, Ὦξος, Ôxos (also called the Amu, Amo River and historically known by its Latin
Latin (, or , ) is a classical language b ...
changing its inflow to the Caspian from the 13th century to the 16th century, caused the coastal towns of
Khazaria
The Khazars ; he, כּוּזָרִים, Kūzārīm; la, Gazari, or ; zh, 突厥曷薩 ; 突厥可薩 ''Tūjué Kěsà'', () were a semi-nomadic Turkic people that in the late 6th-century CE established a major commercial empire coverin ...
, such as
Atil, to flood. In 2004, the water level was below
sea level
Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

.
Over the centuries, Caspian Sea levels have changed in synchrony with the estimated discharge of the Volga, which in turn depends on rainfall levels in its vast catchment basin. Precipitation is related to variations in the amount of North Atlantic depressions that reach the interior, and they in turn are affected by cycles of the
North Atlantic oscillation. Thus levels in the Caspian Sea relate to atmospheric conditions in the North Atlantic, thousands of kilometres to the northwest.
The last short-term sea-level cycle started with a sea-level fall of from 1929 to 1977, followed by a rise of from 1977 until 1995. Since then smaller oscillations have taken place.
A study by the
Azerbaijan Academy of Sciences estimated that the level of the sea was dropping by more than six centimetres per year due to increased evaporation due to rising temperatures caused by
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate variability and change, Climate change in a broader sense also includes ...
.
Environmental degradation
The
Volga River
The Volga (; russian: Во́лга, a=Ru-Волга.ogg, p=ˈvoɫɡə) is the List of rivers of Europe#Rivers of Europe by length, longest river in Europe. Situated in Russia, it flows through Central Russia to Southern Russia and into the Cas ...
, 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
UN Environment Programme warns that the Caspian "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 magnitude of
fossil fuel
A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and combustion, burned as a fuel. The main fossil fuels are coal, petroleum, oil, and natura ...
extraction and transport activity in the Caspian also poses a risk to the environment. The island of
Vulf off
Baku
Baku (, ; az, Bakı ) is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea
The Caspian Sea is the world's largest inland body of water, often described as the List of lakes by area, world's largest ...
, 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 volcano
A mud volcano or mud dome is a landform
A landform is a natural or anthropogenic land
Land, also known as dry land, ground, or earth, is the solid terrestrial surface of the planet Earth that is not submerged by the ocean or other bod ...
es under the Caspian Sea were thought to be the cause of a fire that broke out 75 kilometers from
Baku
Baku (, ; az, Bakı ) is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea
The Caspian Sea is the world's largest inland body of water, often described as the List of lakes by area, world's largest ...
on July 5, 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 Sea will decrease by 9–18 m (30–60 ft) due to the acceleration of evaporation due to
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate variability and change, Climate change in a broader sense also includes ...
and the process of
desertification
Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become increasingly arid. It is the spread of arid areas caused by ...
.
On October 23, 2021, Kazakhstan President
Kassym-Jomart Tokayev
Kassym-Jomart Kemeluly Tokayev ( kk, Қасым-Жомарт Кемелұлы Тоқаев, Qasym-Jomart Kemelūly Toqaev ; born 17 May 1953) is a Kazakhs, Kazakh politician and diplomat who is currently serving as the President of Kazakhstan si ...
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.
Flora and fauna
Flora
The rising level of the Caspian Sea between 1994 and 1996 reduced the number of habitats for rare species of aquatic vegetation. This has been attributed to a general lack of seeding material in newly formed coastal
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
s and water bodies.
Many rare and endemic plant species of Russia are associated with the
tidal areas of the
Volga delta
The Volga Delta is the largest river delta in Europe, and occurs where Europe's largest river system, the Volga River, drains into the Caspian Sea in Russia's Astrakhan Oblast, north-east of the republic of Kalmykia. The delta is located in the C ...
and
riparian forest
A riparian forest or riparian woodland is a forested or wooded area of land adjacent to a body of water such as a river, stream, pond, lake, marshland, estuary, canal, Sink (geography), sink or reservoir.
Etymology
The term riparian comes from ...
s of the
Samur River
The Samur ( rut, Самыр; ; russian: Самур; az, Samurçay) is a river in Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, ...
delta. The shoreline is also a unique refuge for plants adapted to the loose sands of the
Central Asian Deserts. The principal limiting factors to successful establishment of plant species are hydrological imbalances within the surrounding deltas,
water pollution
Water pollution (or aquatic pollution) is the contamination of Body of water, water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and gro ...
, and various land reclamation activities. The water level change within the Caspian Sea is an indirect reason for which plants may not get established.
These affect aquatic plants of the Volga Delta, such as ''
Aldrovanda vesiculosa
''Aldrovanda vesiculosa'', commonly known as the waterwheel plant, is the sole extant taxon, extant species in the flowering plant genus ''Aldrovanda'' of the family Droseraceae. The plant captures small aquatic invertebrates using traps similar ...
'' and the native ''
Nelumbo caspica''. About 11 plant species are found in the Samur River delta, including the unique
liana
A liana is a long-Plant stem, stemmed, Woody plant, woody vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the Canopy (biology), canopy in search of direct sunlight. T ...
forests that date back to the
Tertiary period.
Since 2019
UNESCO
The United Nations Educational, Scientific and Cultural Organization is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) aimed at promoting world peace and security through international coope ...
has admitted the lush
Hyrcanian forests of
Mazandaran, Iran as World Heritage Site under category (ix).
Fauna
The
Caspian turtle
The Caspian turtle or striped-neck terrapin (''Mauremys caspica'') is a species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species ...
(''Mauremys caspica''), although found in neighboring areas, is a wholly freshwater species. The
zebra mussel
The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally Introduced species, introduced to numerous other areas and has become an inv ...
is native to the Caspian and
basins, but has become an
invasive species
An invasive species otherwise known as an alien is an introduced species, introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, i ...
elsewhere, when introduced. The area has given its name to several species, including the
Caspian gull and the
Caspian tern
The Caspian tern (''Hydroprogne caspia'') is a species of tern, with a cosmopolitan distribution, subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic of its genus, and has no accepted subspecies. The genus nam ...
. The
Caspian seal (''Pusa caspica'') is the only aquatic mammal
endemic
Endemism is the state of a species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of or ...
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
Seals may refer to:
* Pinniped
Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammal, marine mammals. They comprise the ext ...
. Today, fewer than 10% remain.
Archeological studies of
Gobustan Rock Art have identified what may be
dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the br ...
s and
porpoise
Porpoises are a group of fully aquatic mammal, aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related ...
s, likely present in the Caspian Sea at least until the
Quaternary
The Quaternary ( ) is the current and most recent of the three period (geology), periods of the Cenozoic era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spa ...
or much more recent periods such as the
last glacial period or
antiquity
Antiquity or Antiquities may refer to:
Historical objects or periods Artifacts
*Antiquities
Antiquities are objects from Ancient history, antiquity, especially the civilizations of the Mediterranean: the Classical antiquity of Greece and Ro ...
. Although the rock art on
Kichikdash Mountain is assumed to be of a dolphin
it might instead represent the famous
beluga sturgeon due to its size (430 cm in length), but fossil records suggest certain ancestors of modern dolphins and whales, such as ''
Macrokentriodon morani'' (
bottlenose dolphin
Bottlenose dolphins are Aquatic mammal, aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan distribution, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. molecular biology, Molecular studies ...
s) and ''
Balaenoptera sibbaldina
''Balaenoptera'' () is a genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of bi ...
'' (
blue whale
The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
s) were presumably larger than their present descendants. From the same artworks,
auks, like
Brunnich's Guillemot could also have been in the sea as well, and these petroglyphs suggest marine inflow between the current Caspian Sea and the Arctic Ocean or
North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...
, or the
.
This is supported by the existences of current endemic, oceanic species such as
lagoon cockles which was genetically identified to originate in Caspian/Black Seas regions.
The sea's
basin (including associated waters such as rivers) has 160 native species and
subspecies
In Taxonomy (biology), biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morphology), but that ca ...
of fish in more than 60
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
.
[Naseka, A.M. and Bogutskaya, N.G. (2009). "Fishes of the Caspian Sea: zoogeography and updated check-list". ''Zoosystematica Rossica'' 18(2): 295–317.] About 62% of the species and subspecies are
endemic
Endemism is the state of a species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of or ...
, as are 4–6 genera (depending on
taxonomic treatment). 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), ]cyprinid
Cyprinidae is a Family (biology), family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barb (fish), barbs and barbel (fish), barbels. Cyprinidae is the largest and m ...
s (32) and clupeid
Clupeidae is a family (biology), family of ray-finned fishes, comprising, for instance, the herrings, shads, sardines, hilsa, and menhadens. The clupeoids include many of the most important food fishes in the world, and are also commonly caught f ...
s (22). Two particularly rich genera are ''Alosa
''Alosa'' is a genus of fish, the river herrings, in the family (biology), family Clupeidae. Along with other genera in the subfamily Alosinae, they are generally known as shads. '' with 18 endemic species/subspecies and ''Benthophilus">tp://ftp.fao.org/docrep/fao/009/ac482e/ac482e27.pdf Subfamily A ...
'' with 18 endemic species/subspecies and ''Benthophilus'' with 16 endemic species.