The largest lake by surface area in the world is the Caspian Sea. Despite its name, the Caspian Sea is technically classified as a lake because it is an enclosed body of water not connected to the world's oceans. It covers an area of approximately 371,000 square kilometers (143,000 square miles). The Caspian Sea is bordered by five countries: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. It has various ecosystems and is home to several unique species, including the critically endangered beluga sturgeon, which is prized for its caviar.