The largest inland body of water by volume is the Caspian Sea. Despite its name suggesting it is a sea, it is classified as a lake due to its enclosed nature. The Caspian Sea is bordered by five countries: Russia, Iran, Azerbaijan, Kazakhstan, and Turkmenistan. It contains a unique ecosystem and is known for its rich biodiversity, including the famous Beluga sturgeon, which produces sought-after caviar. Additionally, the Caspian Sea is significant for its geological resources, including oil and natural gas reserves.