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The Seven Seas
Seas or Lakes?
The Dead Sea and the Caspian Sea are both surrounded by land, with no seawater flowing in or out. Their water is salty so they seem like seas, but really they are lakes.
The Dead Sea is so salty that objects float more easily. The Caspian Sea's salt level is quite a bit lower than ocean waters.
The Black Sea is connected to the ocean by the Turkish Straits. During prehistoric times, this connection sometimes dried up, making the Black Sea a lake.