The Caspian and Aral Sea Basins

The Caspian Sea is the largest inland body of water on Earth by surface area, covering roughly 371,000 square kilometers — larger than Germany — and reaching a maximum depth of about 1,025 meters in its southern basin, a legacy of its origin as a remnant of the ancient Paratethys Sea that separated from the world ocean over five million years ago. Bordered by five states — Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan — the Caspian is legally neither a full "sea" nor an ordinary "lake," a distinction with major consequences for maritime law, since the United Nations Convention on the Law of the Sea would grant coastal states different resource rights depending on which classification applies. This ambiguity was formally addressed only in August 2018, when the five littoral states signed the Convention on the Legal Status of the Caspian Sea at Aktau, Kazakhstan, establishing a hybrid legal regime: national sovereignty over a nearshore zone and shared seabed resources further out, while explicitly barring the naval presence of any non-Caspian state, a clause of particular strategic importance to Russia and Iran.