The Caspian Sea is considered as the largest closed water body on the surface of the Earth. Due to its unique characteristics, the Caspian Sea is considerably fragile against climate changes in recent years. As a result, the population living along the coast of the Caspian Sea has been more exposed to the negative effects of serious climate changes, sea level fluctuations, floods and droughts. Fluctuations in the water level of the Caspian Sea, in addition to environmental challenges, narrow the balance of its transit channels and threaten the geo-economics and environmental security of the Caspian Sea. The decrease in the water of the rivers flowing into the sea is explained by the decrease in the amount of precipitation and by directing the river water to meet the growing demand for agriculture.

The findings indicate that there are very sharp changes in the level fluctuations of the Caspian Sea. According to studies, the level of the Caspian Sea was 2 meters higher 100 years ago. In the 1930s of the 20th century, the level decreased by 1.5 meters, and in the period from 1978 to 1995, there was a rise of 2.7 meters.

Starting from 2005, the sea level drops by 10 centimeters every year. If this change continues for 25-30 years, the North-Eastern part of the Caspian Sea may face the fate of the Aral Sea. Due to its geographical location and lack of connection with the world ocean, the level regime of the Caspian Sea is highly dependent on the rivers that feed it, precipitation and evaporation - the main components of the sea water balance that changes over time.  

All littoral states are concerned about the current state of the environment of the Caspian Sea. Protection of the marine environment and effective use of natural resources are among the priorities of the national policy of the Caspian littoral countries.

In order to minimize the negative impacts on the environment of the Caspian Sea, the "Framework Convention for the Protection of the Marine Environment of the Caspian Sea" was prepared by the experts of the Caspian littoral states with the support of the UN Environment Program and other international organizations.

Discussions of the text of the convention continued during the meetings held from 1995 to 2003 and were signed by the Caspian Sea countries on November 4, 2003. 
The agreement, known as the "Tehran Convention" named after the city where it was ratified, aims at protecting the Caspian environment from all sources of pollution, and also targets the preservation, restoration and protection of the Caspian Sea species and habitats.  The Convention includes provisions on the sustainable and rational use of living resources of the Caspian Sea, on environmental impact assessment and environmental monitoring, as well as research and development.  Driven under the auspices of UNEP within the framework of the CEP and following a fast ratification process by all five Governments of the Caspian littoral states, the Tehran Convention entered into force on 12th August 2006. Later, this date started to be marked as Caspian Day. 
  
The Framework Convention for the Protection of the Marine Environment of the Caspian Sea is the first legally binding regional agreement signed by all five Caspian littoral States, the Republic of Azerbaijan, the Islamic Republic of Iran, the Republic of Kazakhstan, the Russian Federation and Turkmenistan. It lays down the general requirements and the institutional mechanism for environmental protection in the Caspian region.

The Convention on the legal status of the Caspian Sea has been signed at the 5th Summit of the Heads of State of the Caspian littoral states in Aktau, Kazakhstan.

The main purpose of the annual "Day of the Caspian Sea" celebration in the Caspian littoral states is to protect the marine environment from pollution, including the preservation, protection, restoration, sustainable and effective use of biological resources of the Caspian Sea, as well as to inform the population about the matter. In this regard, special importance is attached to "Caspian Day" every year in Azerbaijan, educational activities, including environmental clean-up and landscaping work are carried out with the participation of official state institutions, public organizations, community representatives of the districts located along the Caspian Sea as well as subordinate institutions of the Ministry of Ecology and Natural Resources.

Recommended literature:

1.  Qasımlı, Musa Cəfər oğlu. Azərbaycan Respublikasının xarici siyasəti : 1991-2003 / M. C. Qasımlı ; red. heyəti: A. Əzimov [et al.] ; baş red. E. M. Məmmədyarov ; Azərbaycan Respublikası Xarici İşlər Nazirliyi. - (Azərbaycan Respublikasının diplomatiya tarixi). I hissə. - Bakı : Mütərcim, 2015. - 648 s.
2. Qonaqov, Rufiz Rəhim oğlu. Xəzər hövzəsi və enerji təhlükəsizliyi / R. R. Qonaqov ; elmi red. Ə. M. Həsənov ; Azərbaycan Respublikasının Prezidenti yanında Dövlət İdarəçilik Akademiyası. - Bakı : Elm, 2018. - 200 s.
3. Abbasbəyli, Ağalar Nəriman oğlu. Dünya siyasəti : XX əsrin ikinci yarısı - XXI əsrin əvvəlləri: dərslik / A. N. Abbasbəyli ; elmi red.: Q. H. Məmmədov, R. Ə. Sadıqov. - Bakı : Nurlar NPM, 2011. - 584 s.
4. Каспий : международно-правовые документы: [12 августа 2018 г. главы стран "Каспийской пятерки" подписали в Актау Конвенцию о правовом статусе Каспийского моря, которую называют: "Конституция Каспийского моря" / сост.: С. С. Жильцов [и др.]. - М. : Международные отношения, 2018. - 568 с.