Fed by the Shari and other rivers, the lake has no outlet and its area varies according to the season.
The southern basin of Chad is described under the Shari, which empties its waters into the lake about the middle of the southern shore, forming a delta of considerable extent.
The flood water brought down by the Shari in December and January causes the lake to rise to a maximum of 24 ft., the water spreading over low-lying ground, left dry again in May or June.
There was also at one time communication between the Shari and the Bahr-el-Ghazal, so that the water of the firstnamed stream reached Chad by way of the Bahr-el-Ghazal.
Besides the Shari, the only important stream entering Lake Chad is the Waube or Yo (otherwise the Komadugu Yobe), which rises near Kano, and flowing eastward enters the lake on its western side 40 m.