NYASA, the third in size of the great lakes of Central Africa. It occurs south of the confluence of the two great rift valleys and extends from 9° 29' S. to 14° 25' S. The lake measures along its major axis, which is slightly inclined to the west of north, exactly 350 m., while the breadth varies very little, the maximum being 45 m. about the middle. The total area may be estimated at i i,000 sq.m. The lake lies at an altitude of about 1,65o ft. above the sea. The sides of the valley in which Nyasa lies, which are somewhat irregular towards its southern end, take a decided character of parallel fault scarps in the northern third, and are continued as such beyond the northern extremity. The depth seems to vary between 200 and 400 fathoms, in accordance with the steepness of the shores. The lake receives its water-supply chiefly from the streams which descend from the mountains to the north, all the rest becoming very small in the dry season. Like other lakes of Central Africa it is subject to fluctuations of level, apparently caused by alternations of dry and wet series of years.
At the north-western end is a plain of great fertility, traversed by the Kivira, Songwe and other streams. On the delta of the Rukuru, is the British station of Karonga, the northern port of call for the lake steamers. Southwards the plain narrows, and the sandstone scarp of Mt. Waller rises sheer above Florence bay, the high western plateaux continuing to fall steeply to the water. At Cape Chirombo (I I° 4o' S.) the coast bends to the west, and soon the plateau escarpments recede, and are separated from the lake along its southern half by an undulating plain of varying width, with Bandawe and Kota Kota ports on the coasts. A little north of the latter the Bua river, coming from a remote source on the upper plateau, enters by a projecting delta. At Domira bay the coast turns east, contracting the lake to a narrow neck, with Fort Rifu (west), and Fort Maguire, near Makanjira point (east). Beyond this the lake runs southwards into two bays sep arated by a granitoid peninsula, off which lie several small rocky islands. From the extremity of the eastern bay the Shire makes
its exit to the Zambezi. On the eastern side the escarpments and the boundary fault keep close to the lake, leaving few plains along its shores. In the north-east, the coast is formed by the unbroken wall of the Livingstone range (q.v.). On this coast is the station of Lumbira (Tanganyika Territory). The valley of the Ruhuhu, the only important stream which enters the lake from the east, breaks through the Livingstone range. The formation is here Karroo sandstone, corresponding to that of Mt. Waller on the opposite shore. Just north of the Ruhuhu is Manda, on an excel lent harbour. To the south the wall of mountains recedes some what, and the remainder of the eastern shore shows a variation between rocky cliffs, marshy plains and low hills, to be followed farther south by a wide semicircular bay, generally rock-bound, and ending in Malo point, off which are the largest islands the lake possesses, Likoma and Chisamulu. In the southern half the coast is highest where the Mapangi hills rise to 3,00o ft.
Nyasa, reached in 1859 both by David Livingstone (from the south) and by the German, Albrecht Roscher (from the east), was explored by the former to about 1 r°, and to its northern end by E. D. Young in 1876. From this date onwards it has been the scene of much civilizing work on the part of British missionaries, traders and government officials, and of Germans also. Its shores are divided between Great Britain (with Tanganyika Territory and Nyasaland Protectorate) and Portugal (with Portuguese East Africa). British steamers, including gunboats, have been launched on Nyasa, which forms an important link in the water route from the Zambezi mouth to the heart of the continent. The first detailed survey of its shores was executed by Dr. James Stewart (1876-1877), but this has been superseded by later work.