The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea.It has a surface area of 371,000 square kilometers (143,244 sq mi) and a volume of 78,200 cubic kilometers (18,761 cu mi).he Caspian Sea is the largest inland body of water in the world and accounts for 40 to 44 percent of the total lacustrine waters of the world.