The largest lake by surface area is the Caspian Sea. Despite being referred to as a sea, it is classified as a lake because it is landlocked and does not connect to the world's oceans. The Caspian Sea has an area of approximately 371,000 square kilometers (143,000 square miles) and is bordered by five countries: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. It is known for its unique ecology, containing various species of fish, including sturgeon, which are known for producing caviar. The Caspian Sea also has significant economic importance due to its vast natural resources.