Zambia is a landlocked country located between the southern rim of the Zaire Basin and the Zambezi River. Zambia has land borders with Tanzania to the northeast, Malawi to the east, Mozambique and Zimbabwe to the southeast, Botswana and Namibia to the south, Angola on the west and Zaire to the northwest. Most of the landmass in Zambia is a high plateau lying between 3,500 and 4,500 feet above sea level. In the northeast, the Muchinga Mountains exceed 7,000 ft in height. Elevations under 2,000 ft are found in the valleys of the major river systems. Plateau land in the northeastern and eastern regions is broken by the low-lying Luangwa River., and in the western half by the Kafue River. Both rivers are tributaries of the upper Zambezi, the major waterway of the area. The frequent occurrence of rapids and falls prevents through navigation of the Zambezi. There are three large natural lakes, the Banweulu, Mweru and Tanganyika all situated in the northern region. Lake Bangweulu and the swamps at its southern end cover an area of 3,800 sq miles and are drained by the Luapula River. The Copperbelt, which at one time, was responsible for most of Zambia's wealth, lies in the Western Province, bordering with Zaire.