Second-longest river in Africa (after the Nile), rising near the border of Zambia and the Democratic Republic of Congo (and known as the Lualaba River in the upper reaches) and flowing 4,500 km/2,800 mi to the Atlantic Ocean, running in a great curve that crosses the Equator twice, and discharging a volume of water second only to the Amazon River. The basin of the Congo occupies a vast area of 3,457,000 sq km/1,335,000 sq mi, extending to a maximum of some 1,930 km/1,200 mi from east to west, and the same distance from north to south. The chief tributaries are the Ubangi, Sangha, and Kasai.
Navigation is seriously interrupted by over 30 cataracts in the lower course and by dangerous rapids up to 160 km/100 mi long, notably from the Zambian border to Bukama; below Kongolo, where the gorge known as the Gates of Hell is located; above Kisangani, where the Boyoma Falls (Stanley Falls) are situated; and between Kinshasa and Matadi.
Boma is a large port on the estuary; Matadi is a port 80 km/50 mi from the Atlantic, for ocean-going ships; and at Malebo Pool (formerly Stanley Pool), a widening of the river 560 km/350 mi from its mouth which encloses the marshy island of Bamu, are Brazzaville on the western shore and Kinshasa on the southwestern. The Inga Dam (1976) supplies Matadi and Kinshasa with electricity.
History The mouth of the Congo was seen by the Portuguese navigator Diego Cão in 1482, who established a settlement there. However, the vast extent of its system became known to Europeans only with the explorations of David Livingstone and Henry Stanley in the 19th century.
Its navigation from source to mouth was completed by the expedition in 1974 led by the English explorer John Blashford-Snell, supported by President Mobutu.
Expeditions Nearly 400 years after Diego Cão, a British expedition under Captain Tuckey surveyed the Congo mouth, which was believed to be the outlet of the Niger River, but the expedition ended fatally. Later two expeditions under Cameron and Grady went to the assistance of David Livingstone, who died at Lake Bangweulu. Cameron's expedition led politically to the opening-up of the country under the auspices of King Leopold, and in 1877 Stanley travelled downstream from the Lualaba to the sea.
Source The actual source of the river is still disputed. Geographically the Lubudi, which flows into the Lualaba above Bukama, is the headstream of the river, as from there to the mouth the river valley shows normal development. But if its source is to be found in the headstream of its furthest tributary, the river may be said to rise in a high plateau between lakes Tanganyika and Malawi at an altitude of 1,525 m/5,000 ft.
From the source to the Boyoma Falls Its two headstreams, the Chozi and Chambezi, after their union, enter Lake Bangweulu, and on their exit at the southern corner are known as the Luapula, which soon flows over the Mumbatula Falls. With a breadth varying from 275 m/900 ft to 1,050 m/3,445 ft, the Luapula passes through Lake Mweru (853 m/2,800 ft), and in its journey across the Mitumba Mountains falls some 305 m/1,000 ft. Soon afterwards the main river is joined by the Lualaba and Lubudi, together with two other streams from the west. Up to the Boyoma Falls, two rapids only, those at Nyangwe and Ukassa, make the Congo unnavigable. Stretching now often over 2 km/1.2 mi from bank to bank, it receives from the east the Lukuga, which drains Lake Tanganyika, and further north the Lira and Urindi, coming from the forest tracts.
Middle reaches The middle Congo which enters the alluvial plain of western equatorial Africa at an elevation of 396 m/1,300 ft runs mainly in a westerly direction until it turns sharply southward near Bangala. Of the southern tributaries the Lomami, which pursues a course mostly parallel to the upper Congo, is the chief, whilst the Lulonga joins the main stream many kilometres to the west. Other tributaries on this side are the Ruki and the streams of the great Kasai system, including the Lukeni, Sankuru, Lulua, Ojima, and Kwango. Joining the middle Congo on the right or north bank are the Aruwimi and Ituri, which rise near Lake Albert and drain the equatorial forests, the Rubi and the Ubangi or Welle, which is by far the largest tributary on this side. Below the Ubangi is the Sanga, which flows into the river from the north, and the Kasai which drains much of southern part of the river and enters from the east. There are many lake-like expansions along the middle reaches, the last being that of Malebo Pool, which is 305 m/1,000 ft above sea level, and beside which stand the cities of Kinshasa and Brazzaville. This is the end of the main navigable section of the river which then drops 259 m/850 ft in 235 km/146 mi. Round the unnavigable sections of the river railways have been constructed.
To the Atlantic From Matadi to the Atlantic, which the river finally reaches via a southwesterly course, the distance is about 145 km/90 mi, and may be navigated by ocean-going vessels. The Congo is the only African river with a true estuary, the bottom being a great canyon extending 160 km/99 mi out to sea and reaching in some places a depth of 1,219 m/4,000 ft below the normal sea level. At its mouth the river is 10 km/6 mi wide. While the river is still of great value for navigation the falls which interrupt this are potentially of comparable value for hydroelectricity. With an exceptionally even flow, as waters come equally from north and south of the Equator, the river probably offers 10–15% of the world's power potential.
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