Kafue

The Kafue is the Zambezi's longest internal tributary, a roughly 1,000-km river that runs wholly within Zambia and supplies drinking water to something like 40% of the country, Lusaka included. Its defining feature lies in the middle of its course: the Kafue Flats, a 250-km ribbon of seasonally flooded grassland that swells to 25 mi wide when the rains come, then shrinks back to braided channels and lagoons in the dry months. That annual rise and fall is the engine of the whole system — it is when the largemouth breams, the snail-eating happies and the tilapias move out to spawn. Two hydropower dams, Itezhi-Tezhi above the Flats and Kafue Gorge below, now bracket the floodplain and hold that pulse on a leash.

Geography & hydrology

The Kafue rises near Ndola on the Copperbelt at about 1,1640 ft and runs for roughly 1,0 mi before dropping through the Kafue Gorge into the Middle Zambezi. Its drainage basin covers on the order of 154,0 mi², entirely inside Zambia, which makes it the Zambezi's largest tributary contained within a single country. FEOW treats the Kafue as its own freshwater ecoregion (Ecoregion 557), drawn from central Zambia down to the gorge and taking in two great wetlands — the Kafue Flats and the Lukanga Swamp. The headwaters of the upper Kafue, Lunga, Lufupa and Luswishi are deliberately left out of the ecoregion and folded into the Upper Zambezi Floodplains (Ecoregion 556), because their fish faunas line up more closely with the upper Zambezi than with the Flats below (FEOW Ecoregion 557).

The upper two-thirds of the river is steep enough to run in long stretches of rapids, but those rapids never blocked fish from moving up and down the channel. The real barrier sits at the bottom: the 48-km Kafue Gorge drops through a series of falls that have long kept Middle Zambezi fishes from colonizing the Kafue from below. Between the rapids above and the gorge below lies the Flats — a floor so flat and the gradient so gentle that the river spreads rather than cuts. Hughes and Hughes put the Kafue floodplain at 155 mi long, stretching from Itezhi-Tezhi to the gorge, and as much as 25 mi across at full flood; the FAO survey measured the Flats at around 14,0 mi² of total surface, of which roughly 4,211 mi² sits under water in a wet season and as little as 600–1,373 mi² in the dry (FEOW Ecoregion 557; FAO 1999).

Hydrologically the Kafue behaves as what P.B.N. Jackson called a 'reservoir river': the Flats store the flood and bleed it back slowly, so the main channel never sees the violent surge of a steeper river. Historically the water began rising with the November rains from a dry-season low around 98 ft³/s and peaked in April or May above 1,1640 ft³/s, putting more than 6,0 mi² under water at typical flood — an area roughly ten times Lake Constance. Inundation runs January to June, the floodplain drowned to an average depth of about 10 ft. Two dams now sit at either end. Kafue Gorge dam (148 ft high) closed in 1972 at the downstream lip; Itezhi-Tezhi closed in 1977 upstream, built specifically to regulate inflow onto the Flats so the gorge turbines could run through the dry season. Together they flatten the very fluctuation the floodplain was built around (FAO 1999; Deines et al.).

Water & habitat

The Flats are a floodplain river in the textbook sense — a slow, low-gradient channel threaded through a maze of lagoons, oxbow lakes, abandoned river courses, marshes and levees, with the open river only one element in a shifting mosaic of standing and moving water. Permanent and seasonally flooded ground alike carry dense stands of aquatic plants: hippo grass (Vossia cuspidata), Cyperus papyrus, Typha, Potamogeton and the rice grass Leersia hexandra, with rafts of vegetation known to tear loose from the banks and drift out across open water. That marginal cover is where small and juvenile fish hide, and where the floodplain spawners go when the water comes up (FEOW Ecoregion 557; Ramsar Site 530).

The water itself is moderately mineralized and well buffered, harder than the soft blackwaters of many tropical floodplains. Surveys of the Kafue Gorge reach recorded conductivity from about 140 to 382 µS/cm, dissolved solids of 68–220 mg/L, and pH between roughly 6.7 and 8.2 — a calcium-bicarbonate signature, with calcium running 16–45 mg/L and bicarbonate the dominant anion. Surface temperature swings widely with season and depth, from about 63 °F up to 91 °F and averaging near 75 °F across the year (FAO 1999).

What makes a floodplain like this productive is the yearly handshake between river and floodplain. When the flood spreads over the grassland it picks up nutrients off drowned, decaying vegetation, and the broad warm sheet of shallow water becomes a nursery and a feeding ground all at once. The catch is oxygen: still, plant-choked floodwater over rotting grass can run badly hypoxic, especially where the flood arrives before the dead vegetation has dried and burned off. Pre-dam fisheries biologists understood this well enough that they recommended letting the Flats dry for several weeks and burn before the rains, then raising the reservoir slowly so the aquatic grasses could keep pace — a deliberate effort to keep biological oxygen demand from crashing the next flood. As the water falls, the drowned plain contracts by something like 1,311 mi², concentrating fish into lagoons and channels where predators and fishermen alike can reach them (FAO 1999).

The cichlid fauna

The Kafue's fish fauna is firmly West-Zambezian. FEOW places it in the same aquatic arena as the Okavango, Upper Zambezi and Cunene, with a scattering of species shared with the southern Congo tributaries — the legacy of an old river network repeatedly rearranged by stream capture, in which the Kafue is thought to have once flowed west toward the Okavango before a Middle Zambezi tributary captured it. The Kafue Gorge falls then sealed it off from below, so the Flats fauna is essentially an upper-Zambezi assemblage stranded in its own basin. Endemism at the species level is low — FEOW lists only a killifish, the Kafue killifish (Nothobranchius kafuensis), and a single cyprinid known from one locality — but the Ramsar inventory still counts on the order of 67 fish species across the Flats (FEOW Ecoregion 557; Ramsar Site 530).

The cichlids split cleanly along the lines of the genus Sargochromis, the snail-crushing 'happies,' and their larger piscivorous relatives in Serranochromis. Four Sargochromis carry the atlas roster here, all of them robust, deep-water haplochromines of the Zambezi–Okavango–Kafue system: the Green happy (Sargochromis codringtonii), the Rainbow happy (S. carlottae), Greenwood's happy (S. greenwoodi) and Mortimer's happy (S. mortimeri, described by Bell-Cross in 1975 from this part of the world). These are molluscivores built around their food — codringtonii reaches about 15.5 in and 2.2 kg, hangs in deep, quiet water, slow channels and floodplain lagoons, and grinds prosobranch snails along with water-lily seeds, insects and the odd mouthful of fish scales. Their appetite for snails is concrete enough that codringtonii has been trialled as a biological control agent against the snails that carry schistosomiasis. Like most of their kind they are female mouthbrooders, the female carrying eggs and fry in her mouth (FishBase; Skelton & Teugels 1991).

The roster's lone Serranochromis, the Brownspot largemouth (Serranochromis thumbergi — named for the Swedish naturalist Carl Peter Thunberg), shows how a floodplain predator reads the danger around it. Reaching roughly 13 in and a bit over a kilogram, it takes small fish, insects and snails, builds a scraped sand nest and broods its eggs in the mouth. Where the tigerfish (Hydrocynus) is absent it ranges into open water and even fast rocky stretches; where the tigerfish hunts, the same species retreats into lagoons, backwaters and marshy shallows — the vegetated edges that the flood keeps re-creating every year. Across the genus, the Serranochromis largemouths are the system's resident ambush piscivores, the bridge between the small barbs and tilapias of the grass margins and the open-water predators above them. None of these cichlids is considered threatened: codringtonii and thumbergi both sit at Least Concern on the IUCN Red List, their fortunes tied less to their own biology than to what happens to the flood that organizes the whole floodplain (FishBase; IUCN).

Conservation

Almost every conservation question on the Kafue comes back to the two dams and the pulse they hold between them. Itezhi-Tezhi above and Kafue Gorge below were built to store the wet-season flood and meter it out through the dry season for power — the Kafue system generates around half of Zambia's electricity — and in doing so they shrank the maximum flood, shortened and delayed it, raised the dry-season minimum, and left parts of the floodplain permanently wet or permanently dry that used to flood and drain on schedule. The logic was never subtle: a steady flow is good for turbines, a wildly seasonal one good for fish (FAO 1999).

The biology turned out to be less tidy than either side expected. Early work after impoundment tracked shifts in the catch — declines in the tilapias (Oreochromis macrochir, Tilapia rendalli) against gains in predators — while growth studies on the three-spotted tilapia, Oreochromis andersonii, showed clearly that bigger, longer floods grew bigger fish. But a later, unusually long reconstruction by Deines and colleagues, splicing 25 years of gillnet catches before the 1977 Itezhi-Tezhi closure to 29 years after and modeling a 'no-dam' counterfactual, found no statistically significant effect of the altered flow on total fishery production. What it found instead was a large drop in fish abundance over the 54-year record matched by a large rise in fishing effort in this open-access artisanal fishery. The uncomfortable conclusion: on the Kafue, overfishing has done more to the catch than the dams have, and reducing effort would do more to sustain the fishery than re-plumbing the flood (Deines et al.; FAO 1999).

That does not let the flood regime off the hook — it is the architecture every floodplain spawner depends on, and a clipped flood means less spawning habitat, less drowned-grass productivity and a more permanent, weedier wetland. The reservoir behind Kafue Gorge triggered explosive growth of Vossia cuspidata and other emergent weeds, and Mimosa pigra has since invaded the Flats as a serious pest. Overlaid on this is the pollution coming down from the Copperbelt at the river's source. The Flats do real work scrubbing mine-contaminated water before it reaches Lusaka's taps, but that buffering has limits, and they were overwhelmed on 18 February 2025 when the Sino-Metals Leach tailings dam collapsed upstream and sent an acidic, metal-laden slug down the Kafue. The first assessment recorded crashed pH, copper, iron, zinc, lead and arsenic above Zambian and international limits, contamination in the sediments, bioaccumulation in fish, and widespread fish kills — a single industrial failure doing in days what the dams did across decades. The Kafue Flats are a Ramsar Wetland of International Importance (designated 1991, later enlarged to about 600,500 ha), hold the Lochinvar and Blue Lagoon national parks, and shelter the endemic Kafue lechwe, an antelope built for the seasonal flooding the dams have dampened. The fish, the lechwe and the people who fish the Flats all ride on the same question of whether the river is still allowed to flood (Ramsar Site 530; Chama et al. 2026; WWF Zambia).

Where these cichlids live

Geography & hydrology

Water & habitat

The cichlid fauna

Conservation

Sources

Cichlids recorded here

Sargochromis · 3

Serranochromis · 1