Tchad, Or Tsad, a lake of central Africa, on the borders of Bornoo, Kanem, and Baghirmi, between lat. 12° 30' and 14° 30' N., and lon. 13° and 15° 30' E. It is an irregular triangle, the base of which lies W. S. W. and E. N. E.; length from N. W. to S. E. about 150 m., greatest width about 120 m., area 10,500 sq. m.; but it varies greatly in size in the dry and the rainy season. Its elevation above the level of the sea is about 1,000 ft. It rarely exceeds 15 ft. in depth, and many parts of it are in the dry season a reedy swamp. About two thirds of its area is occupied by islands. Its shores are generally low and flat and covered with rushes and reeds, back of which is fertile ground and rich pasturage; but on the north they rise gradually and are wooded. The S. and W. shores are frequently inundated, and the streets of Kuka, the capital of Bornoo, which stands about 10 m. from the S. W. shore, are sometimes overflowed. Lake Tchad has two large tributaries, the Komadugu on the west and the Shary on the south, but no known outlet. Dr. Nachtigal says that at some former period the surplus waters were discharged through the Bahr el-Ghazal into an extensive lake 300 m.

N. E. The course of this ancient river can still be traced by a fringe of trees, and according to the Arabs water flowed through it for 100 m. during the inundation of 1870. The water of the lake is fresh and sweet; the shallower parts are covered with aquatic plants, and hippopotami, crocodiles, turtles, fish, and water fowl abound. Large herds of antelope feed on its shores, and there are many elephants in the forests on the north. Villages abound on its banks, and the islands in it are densely populated, the central ones by the Buddumas, the eastern by the Kuti, and the northeastern by the Kanembi. The Buddumas are a pagan tribe, distinct from the surrounding Mohammedans. They are well made, active, regular in features, and dark brown or black in complexion. Both sexes are clothed in cotton, and they wear sandals and many ornaments. Cattle and goats are raised by them, and they cultivate maize and cotton. - Lake Tchad was known to Leo Africanus in the 16th century, but the first Europeans who visited it in later times were Den-ham and Clapperton in 1823. Barth, Over-weg, and Vogel explored its vicinity in 1851'5, Rohlfs in 1866, and Nachtigal in 1870.