Lake Malawi or Lake Nyasa, lake in southeastern Africa, located in the Great Rift Valley. Lake Malawi lies between Malawi on the west and Tanzania and Mozambique on the east. It is 580 km (360 mi) long and an average of 40 km (25 mi) wide. The area of the lake has been estimated at 22,490 sq km (8,683 sq mi); its surface is about 472 m (about 1550 ft) above sea level. An outlet of Lake Malawi flows into the Zambezi River. Much of the lake is navigable, and fishing is heavy along its banks. The Scottish missionary and explorer David Livingstone reached the lake in 1859.