Upper Congo

The Upper Congo is the long northern run of the Lualaba River, the headwater Congo that leaves the savannas below the Upemba lakes, swells where the Luvua and the Tanganyika overflow join it, and slides through equatorial forest toward Kisangani. FEOW frames the ecoregion as the slow, island-braided mainstem that ends at the seven cataracts of Boyoma Falls — the old Stanley Falls — where the river finally sheds the name Lualaba and becomes the Congo. Those rapids are a wall: they keep the upper-river fishes apart from the rest of the basin and have left a fauna that is still, by the surveyors' own admission, poorly known and partly undescribed. It is also the river the Wagenya fish from wooden scaffolds at the falls.

Geography & hydrology

FEOW places the Upper Congo as Ecoregion 540, lying entirely within the Democratic Republic of the Congo and running from the base of the Shaba (Katanga) Plateau north to the Upper Congo Rapids ecoregion [539]. The river here is the Lualaba, the name the Congo carries above Boyoma Falls. Its most upstream point in the ecoregion is the confluence where the Luvua — carrying the outflow of Lake Mweru — meets the Lualaba; at that junction the Lualaba roughly doubles in width and its channel fills with long, low islands. About 62 mi downstream the Lukuga River enters, draining the overflow of Lake Tanganyika; the Lukuga is more heavily mineralized than the Lualaba, but its discharge is small enough that it barely shifts the mainstem's chemistry (Bailey 1986; FEOW Ecoregion 540).

The Lualaba starts this run near 2625 ft above sea level and descends gradually to about 1640 ft where it reaches the rapids. It is mostly a wide, slow river, 1–2 mi across in places, broken in only a few reaches. The conspicuous interruption is the 'Portes d'Enfer' — the Gates of Hell — at Kongolo, a roughly 50-km string of rapids from Kimbombo down to Kindu where the gorge pinches to 656–1969 ft wide and the river drops sharply over bedrock. Below that the Lualaba broadens again and takes on the Elila, Ulindi and Lowa, tributaries tumbling out of the eastern highlands that together add something like 2,000–5,0 ft³ per second (Bailey 1986; Hughes & Hughes 1992).

The drama is saved for the very end of the river's upper life. In the adjacent Upper Congo Rapids ecoregion [539], downstream of Ubundu, the Lualaba drops about 197 ft over roughly 62 mi through a chain of cataracts — the Tshungu rapids below Ubundu, the rapids near Wanie-Rukula, and finally the seven steps of Boyoma Falls at Kisangani, each step no more than about 16 ft high but together stretching over 62 mi and ranking among the largest waterfalls on Earth by sheer volume of water moved. The Tshopo and Lindi join just below the falls; the Lomami comes in further down. Geologists read this stair-step as the scar of river capture: the steep Congo is thought to have beheaded the old upper Lualaba, and the rapids are the seam where the two drainages were stitched together (Marlier 1973; Hughes & Hughes 1992; FEOW Ecoregion 539).

Water & habitat

This is equatorial big-river water, warm and forest-fed. The Lualaba runs through savanna in the south and into closed equatorial rainforest in the north, where the canopy climbs to around 148 ft and leaf litter, drowned wood and other allochthonous input from the riparian forest feed much of the aquatic food web (Hughes & Hughes 1992; Bailey 1986). Slow reaches are bordered by riverine forest and swamp, fringed with papyrus (Cyperus papyrus), cattail (Typha domingensis) and floating stands of Nymphaea, with the spongy ambatch Aeschynomene elaphroxylon in the swamp woodland. The flood regime is not a single annual pulse: near the equator the Lualaba is bimodal, with two high-water peaks a year, while some tributaries such as the Elila and Ulindi stay unimodal and the Lowa swings irregularly, tending toward twin maxima around April–May and November–December (Marlier 1973).

The chemistry is soft and near-neutral, the signature of a basin draining old, deeply weathered rock rather than young volcanic or limestone terrain. The cichlids that live here sit comfortably in soft, circumneutral water — the rheophilic Orthochromis stormsi, for instance, is kept around pH 6.5–7.5 and moderate hardness, matching the oxygen-rich currents it favors. The Lualaba's tributaries each carry their own water: the Lukuga arrives more mineralized off Tanganyika, the forest blackwater affluents run darker and more acidic, and the eastern mountain rivers come down cold and clear. Taxonomic exploration of all of it is rated 'poor' by FEOW — surveys are decades old and much historic material sits uncatalogued (FEOW Ecoregions 540 and 539).

Habitat splits sharply between the long slack reaches and the cataracts, and that split organizes the fishes. In the broad, slow river the bottom is sand, silt and sunken wood, worked over by bottom-feeders and sifters; in the rapids of the Portes d'Enfer and the Boyoma chain the water is fast, broken and saturated with oxygen over scoured bedrock and boulder, a world that suits current-loving specialists and bars almost everything else. The cataracts are not just habitat but barrier. Because the rapids isolate the upper river, many fishes common in the Cuvette Centrale downstream never reach the Lualaba, and a set of Nilo-Sudanian fishes — the bichir Polypterus bichir, the climbing perch relative Ctenopoma muriei, Nile tilapia Oreochromis niloticus, the tigerfish ally Ichthyborus besse — persist in the upper Lualaba where the rapids fence them in. The upper river also shares a notable slice of its fauna with the Zambezi, a hint of old drainage connections (Beadle 1981; Banister 1986; Lévêque 1997; Poll 1976).

The cichlid fauna

Set against the rapids radiations of the Amazon or the species flocks of the African Great Lakes, the Upper Congo's cichlid roster is small, riverine and quietly endemic — a handful of mostly modest fishes shaped by slow water, sandy bottoms and the great barrier of the falls. The atlas roster tracks that character. The largest and most distinctly local is Tylochromis elongatus, a sand-sifting cichlid reaching about 6 in that FEOW lists among the ecoregion's endemics; FishBase pins it precisely to the Lualaba 'between Stanley Falls (= Wagenia Falls) and Kindu' — in other words the whole length of this river. It is a maternal mouthbrooder with a heavy, molar-studded pharyngeal jaw, feeding mainly on insects and insect larvae picked from the bottom, the kind of robust benthic generalist that does well in a big, slow, soft-water channel (FishBase; FEOW Ecoregion 540).

Most of the rest are dwarves and small mouthbrooders that hug the substrate. Two belong to Congochromis, the genus Stiassny and Schliewen erected in 2007 for small Congolian cichlids; both are local. Congochromis pugnatus, described from that work, is known only from the middle Congo near Kisangani — the falls reach itself — a roughly 2 in fish still rated Data Deficient by the IUCN, a reminder of how thin the record is. Congochromis squamiceps is the slightly larger, more widespread of the pair, a 2.5–3 in dwarf of the middle-to-upper Congo's larger rivers. Sharing the genus's shaded, slow-water habits is Chromidotilapia schoutedeni, a small biparental-leaning Congo mouthbrooder of clear running water that FishBase records from tributaries at Yangambi, the Wagenia Falls area and the Lualaba — and which the genus revision flagged, with the West African Limbochromis robertsi, as the sister lineage to the Congochromis species (Stiassny & Schliewen 2007; FishBase).

The two current-dwellers complete the picture. Orthochromis stormsi is the rheophile of the group, a 4.5 in cichlid built for fast water: it 'hops' along the bottom rather than swimming in open water, wants high oxygen and strong flow, and turns up in the rapids reaches from Pool Malebo up through the Lindi near Kisangani and into the Lualaba and Lake Mweru region — exactly the broken-water habitat the Portes d'Enfer and the Boyoma chain provide. Pseudocrenilabrus nicholsi is the small, brightly finned mouthbrooder that ranges through this river, recorded from around Yangambi up to the Upemba lakes at the southern edge of the ecoregion; like its relatives it is a maternal mouthbrooder and one of the longest-kept African cichlids in the hobby. None of these is a headline fish the way a peacock or a Tanganyikan shell-dweller is, and that is the point: the cichlids here are a thin, poorly-surveyed, partly-endemic riverine assemblage, outnumbered in the collections by mormyrids, characins and catfishes, and waiting on the modern survey FEOW keeps asking for (FishBase; Seriously Fish; FEOW Ecoregion 540).

Conservation

The Upper Congo's defining conservation fact is how little anyone has looked. FEOW rates taxonomic exploration of both the slow river and its rapids as 'poor,' with surveys decades out of date and much historic material still uncatalogued — so the baseline against which any decline would be measured barely exists. The little recent work there is bears this out. The Decru team's 2017 checklist of the Lindi/Tshopo and the neighboring Itimbiri and Aruwimi — the rivers that join the Congo right at Kisangani — recorded 320 species across the three systems, 187 in the Lindi/Tshopo alone, dominated by elephantfishes (Mormyridae), and showed how waterfalls carve the fauna into upstream and downstream sets — the filtering the Boyoma cataracts impose on the cichlids (Decru et al. 2017; FEOW Ecoregions 540 and 539).

At the falls themselves the human story is the Wagenya. For roughly two centuries the Wagenya (often written Wagenia) have fished Boyoma Falls from an engineered forest of timber: heavy wooden tripods and scaffolds lashed across the cataracts, from which they lower large conical basket traps on vines into the white water. Fish driven downstream wedge into the funnel traps and cannot back out, and the men haul the baskets up hand over hand. It is a fishery found almost nowhere else, tied to one stretch of one river, and it depends on the rapids staying rapids and the runs staying intact — the same falls that shelter the rheophilic Orthochromis and the falls-area Congochromis and Chromidotilapia.

The pressures are the familiar Congo-basin set, sharpened around a fast-growing river city. Kisangani sits at the foot of the falls, and the local fishery is everyday subsistence and market work: studies up the Lualaba at Kindu record cast nets, drift and fixed nets, hooks and longlines taking catfishes, Labeo, Distichodus and Synodontis from a 38-species local catch. Forest clearance for farming along the banks, mining pollution in the upper catchment, and destructive fishing are the recurring threats flagged for the upper-Congo fauna — the same trio the Kundelungu National Park checklist names for the headwater rivers, where 96 fish taxa include many undescribed and several endemics already at risk (Kundelungu checklist 2023; Kindu fishery study; Decru et al. 2017).

Dams are the looming change. The upper Lualaba/Lufira system is the target of the proposed 160-MW Sombwe hydropower dam, sited inside Upemba National Park — one of Africa's oldest — at the head of this ecoregion. A Global Witness investigation found it would flood dryland forest behind a reservoir up to a billion cubic meters, on an assessment a leaked EU-commissioned review called 'seriously flawed,' to power the Katanga copper-cobalt belt; local civil-society groups warn it would strip fishing communities of their livelihood. For a fauna this poorly known, the risk is to lose endemic fishes — some undescribed — before anyone has counted them (Global Witness 2022; FEOW Ecoregion 540).

Where these cichlids live

Geography & hydrology

Water & habitat

The cichlid fauna

Conservation

Sources

Cichlids recorded here

Chromidotilapia · 1

Congochromis · 2

Orthochromis · 1

Pseudocrenilabrus · 1

Tylochromis · 1