Black and white lantern Slide of S.S. on Nyassan - British South Africa. Part of Box 288, British South Africa. Boswell Collection. Slide number 21 S.S. on Nyassa - Nyassa is possibly - Lake Malawi (Lake Nyasa, or Lago Niassa in Mozambique), is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. The third largest and second deepest lake in Africa, it is also the ninth largest in the world.