The Caspian Sea is a geographical paradox, a massive body of water that defies simple classification as either a lake or a sea. Situated at the crossroads of Europe and Asia, this landlocked expanse is the largest inland water body on Earth. Its immense scale has shaped the history, ecology, and politics of the surrounding region. The Caspian Sea’s distinct characteristics, from its uncertain legal status to its dramatically fluctuating water levels, illustrate a unique interaction between geological history and human activity.
Defining the World’s Largest Inland Water Body
The Caspian Sea holds the title of the world’s largest inland body of water by both surface area and volume, covering approximately 371,000 square kilometers. Its size, roughly equivalent to the entire country of Japan, led ancient cultures to refer to it as a sea. It contains about 78,200 cubic kilometers of water, which is a third of all the non-oceanic water on the planet.
Geologically, the Caspian is a relict basin, a surviving remnant of the ancient Paratethys Ocean that once stretched across Eurasia millions of years ago. Tectonic shifts isolated it, severing its connection to the global ocean system. This history explains its unique salinity: its waters are brackish, with a salt concentration of about 1.2 percent. This makes it significantly saltier than a freshwater lake but only about one-third the salinity of the open ocean. Since it is an endorheic basin, meaning it has no outlet, water loss occurs only through evaporation, which contributes to the gradual accumulation of minerals and salt.
Wildlife Found Nowhere Else on Earth
The evolutionary isolation of the Caspian Sea has fostered a fragile ecosystem rich in endemic species. The most notable example is the Caspian Seal (Pusa caspica), the only marine mammal found in this water body. These seals, which give birth on the ice floes of the northern Caspian in winter, have seen their population plummet from over one million a century ago to fewer than 70,000 individuals today.
The Caspian is also significant as the habitat for six endemic species of sturgeon, including the famed Beluga sturgeon. These ancient, slow-maturing fish are the source of the world’s most prized caviar, a demand that has driven them toward the brink of extinction. The sturgeon population has dropped by an estimated 90 percent over the past four decades, primarily due to habitat degradation and poaching for their roe.
Declining water quality from industrial pollution and the loss of shallow breeding grounds due to water level changes have severely impacted both the seals and the sturgeon. Oil extraction activities disrupt the food chain and introduce toxins. The seals, listed as Endangered, face the threat of losing up to 81 percent of their vital winter breeding ice if water levels continue to fall dramatically.
Rapid and Dramatic Water Level Changes
The Caspian Sea is characterized by dramatic fluctuations in its water level, independent of global sea level changes. Historically, the water level has been known to rise and fall by several meters over the course of a few decades. The current trend is a concerning decline, with the surface level falling by approximately seven centimeters each year.
The primary drivers of these fluctuations are the balance between river inflow and evaporation rates. The Volga River provides nearly 80 percent of the Caspian’s water, making its flow rate a major factor. Rising surface temperatures due to climate change are increasing evaporation, which is not being sufficiently offset by precipitation or river discharge.
This drop has profound geographical and economic consequences, particularly in the shallow northern regions. A projected decline of nine to eighteen meters by the end of the century could uncover vast stretches of the seabed, potentially stranding ports and coastal infrastructure. The retreat of the water also threatens to dry out protected wetlands and coastal lagoons that are crucial spawning grounds for fish and migratory birds.
A Sea Divided by Five Nations
The Caspian Sea is bordered by five nations: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. Following the collapse of the Soviet Union, the status of the sea became a point of geopolitical tension among these littoral states. The central dispute revolved around whether the Caspian should be treated legally as a lake or a sea, as this distinction determines how its resources are divided.
If classified as a lake, international law would suggest an equal division of the surface and seabed among the five nations, granting each a 20 percent share. If classified as a sea, the UN Convention on the Law of the Sea would apply, allowing for territorial waters and exclusive economic zones. This model would favor states with longer coastlines. The disagreement was intense because the seabed contains massive reserves of oil and natural gas.
After decades of negotiation, the five nations signed the Convention on the Legal Status of the Caspian Sea in 2018, establishing a “special legal status.” This compromise grants each country exclusive control over a 15-nautical-mile territorial water zone and an additional 10-nautical-mile exclusive fishing zone. The agreement stipulated that the division of the seabed’s mineral resources would be determined by separate agreements, allowing hydrocarbon development to proceed while maintaining shared access to the central waters.