Lake Copais, Kopais, or Kopaida (; ) is a former lake in the centre of Boeotia, Greece, west of Thebes. It was drained in the late 19th century. The area where it was located, though now a plain, is still known as Kopaida.

Lake Copais, Kopais, or Kopaida (; ) is a former lake in the centre of Boeotia, Greece, west of Thebes. It was drained in the late 19th century. The area where it was located, though now a plain, is still known as Kopaida.