It is the largest enclosed body of water on Earth, big enough to have its own name in a dozen languages and a coastline shared by five nations. It contains seals, sturgeon and vast reserves of oil and gas. And for more than two decades, the countries that surround it could not agree on what, in law, it actually was. Was the Caspian a sea, or was it a lake? The question sounds like pedantry. In fact billions of dollars, drilling rights and the right to sail warships all rode on the answer.
The Caspian sits in a great depression between Europe and Asia, its surface lying some 28 metres below the level of the world ocean. It covers around 371,000 square kilometres — larger than Germany — and holds by far the greatest volume of any inland water. It is fed chiefly by the Volga, Europe's longest river, and drains nowhere; water leaves only by evaporation, which is why it is mildly salty, roughly a third as saline as the open ocean. Landlocked, brackish and immense, it genuinely straddles the definitions. Its northern shallows freeze in winter while its southern reaches stay temperate, and it shelters its own endemic wildlife, among them the small Caspian seal and the beluga sturgeon whose roe is prized as the world's most expensive caviar.
Why the label mattered
The stakes turn on international law. The rules that govern seas — principally the UN Convention on the Law of the Sea — grant each coastal state a band of territorial waters and an exclusive economic zone, with the seabed carved up accordingly. The rules for a lake are different: a shared lake is generally treated as common property, to be divided by agreement among the states around it, often into equal shares. Under the Soviet Union the matter never arose in earnest, because only two states bordered the water: the USSR and Iran, who split its use between them by treaty.
That tidy arrangement shattered in 1991. The collapse of the Soviet Union turned two Caspian neighbours into five overnight: Russia and Iran were now joined by newly independent Azerbaijan, Kazakhstan and Turkmenistan. Each wanted the largest possible slice of a seabed known to hold enormous petroleum wealth. If the Caspian were a sea, a country with a long coastline — Kazakhstan, say — could claim a correspondingly large economic zone. If it were a lake to be divided equally, Iran, with the shortest Caspian shoreline, stood to gain a bigger share than its coast alone would justify. Predictably, Iran favoured the lake reading and others leaned towards sea principles. The dispute simmered for years, tangling oil consortiums, pipeline routes and naval build-ups in legal limbo.
A convention, and a fudge
Resolution came slowly. After years of negotiation, the five states signed the Convention on the Legal Status of the Caspian Sea at Aktau, in Kazakhstan, in August 2018 — some twenty-two years after formal talks began. The convention's cleverness lay in refusing the binary altogether. The Caspian was granted, in effect, a special legal status of its own: neither fully sea nor fully lake. The surface waters would be shared for free navigation and fishing, much as a lake might be, while the seabed and its resources would be divided into national sectors between neighbouring states, more in the manner of a sea. Crucially, the signatories agreed that no outside military forces could be stationed on the Caspian — a provision that mattered greatly to Russia and Iran, who wanted no foreign navies on their shared water.
The Aktau convention did not settle everything; some seabed boundaries between the southern states were left for further bilateral talks, and the delimitation between Azerbaijan, Iran and Turkmenistan in the resource-rich south remained the touchiest of them. But it broke the deadlock that had frozen the region's grandest resource question since the Soviet collapse, and cleared the legal ground for the pipelines that carry Caspian oil and gas west towards Europe and Turkey.
There is a final twist that makes the whole debate feel almost poetic. The Caspian takes its name from the ancient Caspi people who once lived on its south-western shore, and it was one of the first great waters the classical geographers tried to map. It has been called a sea for millennia in ordinary speech. It took modern lawyers, oil and the hard arithmetic of national self-interest to ask whether the name was really true — and then to decide, wisely, not to answer.
Quiz nuggets
- The Caspian is the largest enclosed body of water on Earth, covering around 371,000 square kilometres and lying about 28 metres below sea level.
- Its surface is mildly salty — roughly a third as saline as the open ocean — and it is fed mainly by the Volga.
- Before 1991 only two states bordered it, the USSR and Iran; the Soviet collapse raised that to five, adding Azerbaijan, Kazakhstan and Turkmenistan.
- Whether it was legally a sea or a lake determined how its huge oil and gas reserves would be divided.
- The 2018 Convention on the Legal Status of the Caspian Sea, signed at Aktau, gave it a special status and barred outside military forces.