Mozambique is 44% coastal lowlands, rising toward the west to a plateau 150 to 610 m (500–2,000 ft) above sea level and on the western border to a higher plateau, 550 to 910 m (1,800–3,000 ft), with mountains reaching a height of nearly 2,440 m (8,000 ft). The highest mountains are Namuli (2,419 m/7,936 ft) in Zambézia Province and Binga (2,436 m/7,992 ft) in Manica Province on the Zimbabwean border. The most important rivers are the Zambezi (flowing southeast across the center of Mozambique into the Indian Ocean), the Limpopo in the south, the Save (Sabi) in the center, and the Lugenda in the north. The most important lake is the navigable Lake Malawi (Lake Niassa); Lake Cahora Bassa was formed by the impoundment of the Cahora Bassa Dam. In the river valleys and deltas, the soil is rich and fertile, but southern and central Mozambique have poor and sandy soil, and parts of the interior are dry.