DR Congo's geography: a river basin with one narrow way out

How almost the whole country drains through one river

Most of the Democratic Republic of the Congo lies inside the hollow of the Congo River basin, and the river system serves nearly every part of it. The Wikipedia geography article lists three exceptions, all of them small. The north-east of the Mayombe hills in Kongo Central drains through a short coastal river called the Shilango. A strip of the eastern border beside Lakes Edward and Albert belongs to the Nile basin. And a small piece of the extreme south-east lies in the Zambezi basin and sends its water to the Indian Ocean. Everything else, from the Ubangi in the north to the Katanga plateaus in the south, ends up in one channel.

That channel meets the sea at the far western tip of the country, at the end of a partly forested panhandle that the Wikipedia geography article describes as an extension of the southern uplands, dropping sharply to a very narrow shore. The coastline is 37 km long in the World Factbook data that Wikipedia reproduces; the prose of the same article puts it at about 40 km. The river and that strip of shore on its north bank are the country's only outlet to the Atlantic. North of the strip lies Cabinda, an exclave of Angola, and south of the river lies Angola itself, so the estuary is a frontier along its whole length. Britannica gives that length as 134 km, from Matadi to the sea.

The land boundary is long by comparison, 10,481 km in the same Factbook data, and the two longest sections run along the south-west and south-east.

Set side by side, the figures describe the country's shape. More than 10,000 km of land frontier enclose 2,344,858 km², and the ocean touches that area along a stretch of shore shorter than the estuary leading to it. The Tanzanian section is drawn across water, down Lake Tanganyika. Beyond the river mouth the channel keeps going under the sea: Britannica traces a deep submarine canyon running about 200 km offshore.

What lies in the shallow bowl at the centre

The core of the country is the central Congo basin, often called the cuvette, literally a saucer or shallow bowl. Wikipedia puts it at roughly 800,000 km², about a third of the national territory.

Its height is where the references on file part company. Britannica describes a vast rolling plain at an average of about 520 metres above sea level, with a lowest point of 338 metres at Lake Mai-Ndombe and a highest of 700 metres in the hills of Mobayi-Mbongo and Zongo in the north. The Wikipedia geography article gives the basin an average elevation of about 44 metres, which would put the average lower than the lowest point Britannica records. Britannica's three figures agree with one another, and they are the ones this page uses.

The bowl has been filling for a long time. Boreholes have shown sediment accumulating in it since late Precambrian times, at least 570 million years ago, worn from the formations around its rim. Britannica's article on the river reads the layout, with relief, thick deposits and bedrock arranged like an amphitheatre around the main channel, as evidence of a persistent tendency to subside. The edges rise as the centre sinks, and the uplift is strongest on the eastern side, where the Western Rift Valley also formed.

Water covers a large share of the floor. Much of the forest inside the basin is swamp, and more of it is a mixture of marsh and firm ground. Lakes Tumba and Mai-Ndombe in the west of the basin are, in both references, what remains of a much larger body of water. Britannica suggests the basin may once have been an inland sea; Wikipedia describes a huge interior lake that filled it until the Congo breached the edge and drained the interior.

The soils follow the water. In the warm, humid lowlands the equatorial soils sit under thick forest and stay almost fixed in place, because there is so little erosion beneath the canopy, and in the swamps a very thick soil is fed constantly by humus. The savanna soils on the higher ground around the basin erode more readily, although the valleys cut through them carry rich alluvium.

Why the river crosses the equator twice

Britannica traces the Congo to the Chambeshi, which rises in the highlands of north-eastern Zambia between Lakes Tanganyika and Nyasa. Inside the country the upper river is usually called the Lualaba. It runs north out of the Katanga plateaus and then bends west and south-west in a great counterclockwise arc, crossing the equator twice before it turns down towards Kinshasa and the sea. Britannica gives the river a length of 4,700 km and its drainage basin an area of 3,457,000 km², a figure its country article rounds to 3,460,000.

The arc explains how the river behaves. About a third of the country lies north of the equator and two thirds south of it, and the seasons on the two sides run opposite each other. In the north the dry season falls roughly between early November and late March, which is the rainy season in the south. Tributaries on one side of the line are running high while those on the other are low, so the main channel is supplied from one hemisphere or the other all year, and its flow is unusually regular.

The alternation is driven by the intertropical convergence zone, the belt where the trade winds of the two hemispheres meet and force moist air upward until it condenses as heavy rain. Britannica follows it across the country through the year. In July and August the zone of heaviest rain lies over the north. In September and October it crosses central Congo. Between November and February the south receives its maximum, and the zone then moves north again, crossing the centre in March and April. The middle of the country therefore gets two rainfall maxima a year, and a number of places on both sides of the equator have two wet seasons and two dry ones. The extreme eastern highlands lie outside the zone's path and answer to the south-east trade winds alone.

The river widens as it gathers. Wikipedia gives a width of 10 km at the mid-point of its length. Britannica's figures run from more than 5.5 km below Isangi, where the Lomami comes in, to 8 to 11 km further down, and 13 km at the mouth of the Mongala. The average flow climbs from less than 7,000 cubic metres a second at Kisangani to close to its maximum by Kinshasa, after the Ubangi and the Sangha have joined from the right bank and the Kwa from the left.

Where the river carries boats and where it stops

Falls and rapids cut the Congo into separate reaches, and the country's river towns grew at the breaks between them.

How the interior river is divided

On the upper river several streams of similar size unite within about 100 km: the upper Lualaba takes in the Luvua and then the Lukuga. Each widens into a lake or something close to one along its course, Lake Upemba on the Lualaba and Lake Mweru on the Luvua system, and rapids interrupt the main stream in several places. Only boats of low tonnage can work these sections, and water hyacinth threatens to choke them.

Kisangani, just below Boyoma Falls, a series of seven cataracts, is where the navigable river properly begins. From there the middle Congo runs for more than 1,600 km through its alluvial plain, split into arms by strings of islands, to within 35 km of Kinshasa. The last stretch, the Chenal or Couloir, squeezes it between banks less than 2 km apart and cuts several hundred metres down into the soft sandstone of the Batéké Plateau. Then it opens into Malebo Pool, about 24 by 27 km, with Bamu Island at its centre covering 181 km². Kinshasa and Brazzaville face each other across it.

Why the capital stands above the cataracts

Britannica describes Malebo Pool as the point where river traffic sets out for the interior, and immediately below it the first falls begin. The lower Congo drops from a little under 275 metres to a few metres above sea level through two series of cataracts and rapids separated by a calmer reach, 32 cataracts in all including Inga Falls. Wikipedia names the whole sequence the Livingstone Falls. Below them is Matadi, the main port, where the estuary starts. Between Matadi and Boma the channel is 20 to 24 metres deep, but further down, where islands split the river, it falls to 6 to 7.5 metres in places and has to be dredged for ocean ships.

Kinshasa grew at that hinge between the open river and the falls. Britannica counts 5,000 people there in 1889, 28,000 in 1925, 250,000 in 1950, 1,500,000 in 1971 and about 4,700,000 in the mid-1990s. The record gives 14,565,700 for 1 July 2020.

The same drop is the country's power supply. A hydroelectric dam at Inga Falls near Matadi was completed in 1972 and its second stage in 1982, and in the 2020s almost all the electricity generated in the country was hydroelectric, according to Britannica.

How the rift raises the eastern border

The ground rises and breaks up in the east. The eastern highlands run for more than 1,500 km from above Lake Albert to the southern tip, between 80 and 560 km wide, with hills and mountains from about 1,000 metres to more than 5,000. Their eastern edge is the Western Rift Valley, the western arm of the East African Rift System, and the border runs down it through Lakes Albert, Edward, Kivu and Tanganyika to Mweru. The Mitumba Mountains follow the rift, rising to 2,990 metres.

Between Lakes Albert and Edward, astride the Ugandan border, stands the Rwenzori Range. Its summit, Margherita Peak on Mount Stanley, is the country's highest point at 5,109 metres, and it carries permanent glaciers and snow. On some of the Rwenzori slopes a falling mist hangs almost constantly. The Congolese side of the massif lies inside Virunga National Park, which holds about a fifth of it and shares the summit with Uganda's Rwenzori Mountains National Park across the line.

Which way the eastern lakes drain

The rift lakes do not all send their water the same way. Lake Kivu drains south through the Ruzizi into Lake Tanganyika, and Tanganyika empties through the Lukuga into the Lualaba, so both belong to the Congo. Edward and Albert, the two northernmost, drain north into the Nile basin. A line of lakes along a single border therefore divides between the Congo and the Nile, and the strip of ground beside Edward and Albert is one of the three corners of the country that the Congo does not drain.

What the Virunga volcanoes did to Goma

North of Lake Kivu the volcanic Virunga Mountains stretch across the rift. UNESCO counts eight volcanoes in the massif, seven of them wholly or partly inside the park, and two of them, Nyamuragira and Nyiragongo, account between them for two-fifths of the historic volcanic eruptions recorded on the African continent. Their alkaline lava is extremely fluid. The crater of Nyiragongo holds a lake of almost permanent lava that empties from time to time.

It emptied on 17 January 2002. Three streams of lava ran out at 64 km/h, each about 46 metres wide, and one of them went straight through Goma, killing 45 people and leaving 120,000 homeless. More than 400,000 people were evacuated. The lava crossed the airport, destroyed a runway and ran into Lake Kivu, poisoning the water. Six months later Nyamuragira erupted as well.

The lava also made the soil. Parts of the Great Lakes highlands are covered with rich soil derived from it, and the eastern highlands grow yams, beans and sweet potatoes for food, with arabica coffee and tea for export.

What the plateaus around the basin are like

High plateaus close in the central basin on nearly every side except the east. To the north, the Ubangi-Uele plateaus rise to between 915 and 1,220 metres and form the divide between the Nile and Congo basins; they also separate the central basin from the plains draining to Lake Chad. The northern uplands as a whole average about 600 metres, rising to 900 where they meet the eastern highlands, and are covered largely in savanna, with woodland rare.

The southern uplands are broader, about a third of the country, as large as the basin itself. They slope from about 1,000 metres near the Angolan border down to about 500 near the basin. The cover is more varied than in the north: woodland in some places, savanna grass in others, and long gallery forests along the streams feeding the Kasai.

In the far south-east the Katanga plateaus stand higher. Their ridges include Kundelungu at 1,600 metres, Mitumba at 1,500 and Hakansson at 1,100, and they reach as far north as the Lukuga, taking in the Manika Plateau, the Kibara and Bia mountains and the high plains of Marungu. The Upemba depression in the same region has been on UNESCO's tentative list since 1997. Wikipedia credits the rift with exposing mineral wealth across the south and east and names cobalt, copper, diamonds, gold, tin and uranium among the deposits, especially in Katanga. Lubumbashi is the capital of the copper-mining zone and Mbuji-Mayi, in Eastern Kasai, the diamond centre.

On the western side, the northern escarpment of the Angola Plateau rises in the south-west, and the far west holds a coastal plateau with the hill country of Mayumbe and the Cristal Mountains, below which a narrow coastal plain runs to the Atlantic.

Settlement leans towards the savanna. Britannica describes about half the population as rural, mostly in scattered villages, with the savanna woodlands of the south-central regions the most populous, and to some extent the coast. The record counts 105,789,731 people for 1 January 2023.

How the climate changes from forest to mountain

Three broad regimes cover most of the country: tropical rainforest in the river basin, tropical wet-and-dry in the southern uplands, and tropical highland in the east above 2,000 metres. Britannica adds a fourth, confined to the west coast and shaped by low ground and the cold Benguela Current. Its stations give the spread.

The equatorial forest has the highest and steadiest temperatures, with daytime highs between 30 and 35 °C and nights that rarely drop below 20 °C, and the annual average across the country is about 25 °C. Rain falls there throughout the year. Annual totals across the country run from about 1,000 to 2,000 mm, highest in the heart of the basin and in the highlands west of Bukavu, and they fall away with distance from those two areas.

North and south of the equatorial core the dry season lasts from four to seven months, usually April to October on the southern side, depending mostly on how far a place lies from the equator. Even in the rains, short dry spells of several weeks can occur. The far south-east, the old Katanga, has cool, dry winters and warm, damp summers, and parts of it are the only areas with dry seasons of four to five months and occasional drought. Along the chain of lakes from Albert to Tanganyika the air is moist and the temperature range narrow, and humidity on the mountains climbs with altitude until it reaches saturation.

Which forests and animals the parks protect

Forest is the default cover. The World Bank, in the framework guiding its work for 2022 to 2026, describes rainforest across 67% of the country, holding an estimated 85 billion tons of carbon dioxide equivalent; Britannica's economy article says the forest reserves cover more than half. In the heart of the basin the trees reach 40 to 50 metres, and the timber species include mahogany, ebony, limba, wenge, agba, iroko and sapele. Mangroves take over in the coastal swamps and at the river mouth, and on the highest eastern mountains the forest gives way to bamboo thickets and Afro-Alpine vegetation.

The river is a boundary for animals as well as for states. Bonobos live only in the lowland rainforest along the south bank of the Congo, and Wikipedia records the country as the only one where they are found in the wild. Chimpanzees live mostly in the equatorial forest, and gorillas in the eastern mountains around Lake Kivu. The okapi, which UNESCO lists as endemic to the country, lives in the primary forests of Uele, Aruwimi and Ituri in the north, and giraffes mostly in the north-eastern grasslands.

The country ratified the World Heritage Convention on 23 September 1974, and all five of its listed properties are natural sites.

• Virunga National Park, inscribed 1979, a national park since 1925 and delimited by a 1954 ordinance over 790,000 hectares, from 680 metres up to 5,109
• Garamba National Park, inscribed 1980, savanna and woodland near the South Sudanese border
• Kahuzi-Biega National Park, inscribed 1980, north of Bukavu, with populations of eastern lowland gorillas
• Salonga National Park, inscribed 1984, rainforest in the central basin
• Okapi Wildlife Reserve, inscribed 1996, which protects part of the okapi population still living in the wild

Lomami National Park went onto the tentative list in 2024. Against the listings stands the clearing. Wikipedia reports that the rate of deforestation doubled between 2015 and 2019 and rose by a further 5% in 2021, driven by slash-and-burn farming and illegal logging, and that the government established the Kivu-Kinshasa Green Corridor in January 2025 with the stated aim of protecting a large part of the basin forest.