NYASA, the third in size of the great lakes of Central Africa, occupying the southern end of the great rift-valley system which traverses the eastern half of the equatorial region from north to south. Extending from 9° 29′ to 14° 25′ S., or through nearly 5° of latitude, the lake measures along its major axis, which is slightly inclined to the west of north, exactly 350 m., while the greatest breadth, which occurs near the middle of its length, between 11° 30′ and 12° 20′ S., is 45 m. In the northern and southern thirds of the length the breadth varies generally from 20 to 30 m., and the total area may be estimated at 11,000 sq. m. The lake lies at an altitude of about 1650 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 fault scarps in the northern third, and are continued as such beyond the northern extremity. Apart from the recent alluvium on the immediate shores, the lake lies almost entirely in granite and gneiss formations, broken, however, by a band of horizontally-bedded sandstones, which cuts the axis of the lake in about 10° 30′ S., the flat-topped, terraced form of the latter contrasting strangely with the jagged or rounded outlines of the former. Near the margin, overlying the sandstones, there are beds of limestone with remains of recent molluscs, pointing, like the raised beaches which occur elsewhere, to an upward movement of the coasts. Lacustrine deposits up to 700 ft. above the present lake-level have been discovered. Geologically, the lake is believed to be of no great age, a View supported by topographical evidence. The depth of the lake seems to vary in accordance with the steepness of the shores, increasing from south to north. The greater part of the northern half shows depths of over 200 fathoms, while a maximum of 430 fathoms was obtained by Mr. J. E. S. Moore in 1899, off the high western coast in about 11° 40′ S. A more complete series of soundings, however, since made by Lieut. Rhoades, and published in the Geographical Journal in 1902, gives a maximum of 386 fathoms off the same coast in 11° 10′ S. 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, rising either among the volcanic masses to the north or on the western plateau. Just north of 19° S. on the delta ot the Rukuru, is the British station of Karonga, the northern port of call for the lake steamers, though with but an open roadstead. Southwards the plain narrows, and in about 101/2° S. the sandstone scarp of Mount Waller rises sheer above the indentation of Florence Bay, the high western plateaus continuing to fall steeply to the water in wooded cliffs for more than 80 m. In this stretch occur the land-locked bays of Ruarwe (11° 5′ S.) and Nkata (11° 36′ S.), and the mouth of the Rukuru (10° 43′ S)., which drains the plateau from south to north. At Cape Chirombo (11° 40′ 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. In 11° 56′ S. is the British station of Bandawe, and in 12° 55′ that of Kota Kota, on a lake-like inlet, forming a sheltered harbour. 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, in 13° 35′, the coast turns suddenly east, contracting the lake to a comparatively narrow neck, with the British stations of Fort Rifu on the west, and Fort Maguire, near the headland of Makanjira Point, on the east. Beyond this the lake runs southwards into two bays separated by a granitoid peninsula, off which lie several small rocky islands. On this peninsula was placed the mission station of Livingstonia, the first to be established on the shores of Nyasa. From the extremity of the eastern bay the Shire makes its exit to the Zambezi. On the eastern side the plateau escarpments keep generally close to the lake, leaving few plains of any extent along its shores. The crest of the eastern watershed runs generally parallel to the shore, which it approaches in places within 20 m. From the north point to 10° 30′ S. the coast is formed by the unbroken wall of the Livingstone or Kinga range, rising where highest (9° 41′ S.) fully 6000 ft. above the water. Du this coast, on a projecting spit of land, is the German station of Old Langenburg, some 10 m. from the northern extremity. In 10° 30′ the plateau is broken by the valley of the Ruhuhu, the only important stream which enters the lake from the east. The formation is here sandstone, corresponding to that of Mount Waller on the opposite shore. just north of the Ruhuhu is the German station of Wiedhafen, on an excellent harbour, formerly Amelia Bay. South of the Ruhuhu the wall of mountains recedes somewhat, and the remainder of the eastern shore shows a variation between rocky cliffs, marshy plains of restricted area and groups of low hills. In 11° 16′ is the deep inlet of Mbampa Bay, offering a sheltered anchorage. South of it the coast forms a wide semicircular bay, generally rock-bound, and ending south in Malo Point (12° 10′ S.), off which are the largest islands the lake possesses, Likoma and Chisamulu, the former measuring about 4 m. by 3. In the southern half the coast is highest in about 13° 10′ S., where the Mapangi hills rise to 3000 ft.

Nyasa, reached in 1859 both by David Livingstone (from the south) and by the German traveller Albrecht Roscher (from the east), was explored by the former to about 11°, 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 (principally Scottish) missionaries, traders and government officials, and, in more recent years, of Germans also. Its shores have been divided between Great Britain, Portugal and Germany, Great Britain holding (within the British Nyasaland Protectorate) all the west coast south of the Songwe, and the southern extremity of the east coast (south of 111/2° S.); Portugal the rest of the east coast south of 111/2° S.; and Germany the remainder. British steamers, including two or three 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. Germany also has a gunboat on the lake. The first detailed survey of its shores was executed by Dr James Stewart (1876–1877), but this has been superseded by later work, especially that of Lieuts. Rhoades and Phillips.

See Proc. R.G.S. (1883), p. 689; Geogr. Journal, vol. xii. p. 580; J. E. S. Moore, ib. vol. x. p. 289, and “The Geology of Nyasaland,” by A. R. Andrew and T. E. G. Bailey, with note on fossil plants, fish remains, &c., by E. A. N. Arber and others and bibliography in vol. 66 of Quart. Jnl. Geog. Society (May 1910).  (E. He.)