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The northern Cephissus river (Greek Êçöéóóüò: Kifissós, Kephissós, or Kêphissos) or Cephisus (Greek Êçöéóüò: Kêphisos) rises at Lilaea in Phocis and flows by Delphi through Viotia and eventually issues into Lake Copais which is therefore also called the Cephisian Lake. This Cephissus is the modern Mauro Potamo (Black River).

Pausanias (9.38.7) records a Theban tradition that the river Cephissus formerly flowed under the a mountain and entered the sea until Heracles blocked the passage and diverted the water into the Orchomenian plain.

http://en.wikipedia.org/wiki/Cephissus_(Boeotia)