At sunrise on Lake Victoria, floating cages, giant square enclosures suspended just below the water’s surface, now dot the shoreline from Jinja in Uganda to Kisumu in Kenya, replacing the traditional nets of many local fishermen in search of Nile perch and tilapia.

Within them, a new aquaculture frontier thrives as millions of fingerlings are fattened into table-sized fish, feeding East Africa’s growing appetite for animal protein.

For policymakers, these cages symbolise progress—a response to collapsing wild fish stocks, an answer to soaring youth unemployment, and a pillar of the “blue economy.”Driven by dwindling capture fisheries, aquaculture has become one of the fastest-growing food sectors globally. Uganda, for instance, has seen cage aquaculture production jump from just 800 tonnes in 2006 to more than 138,000 tonnes in 2021, a staggering increase fuelled largely by Nile tilapia farming.

Across Lake Victoria, the floating cage technology now supports at least 60,000 jobs, up from 34,000 two decades ago. Globally, the sector employs more than 61 million people, and East African governments view it as a cornerstone of their blue economy strategies.

A 2022 hydro-acoustic survey by the East African Community’s Lake Victoria Fisheries Organisation (LVFO) reported that Nile perch stocks stood at 333,341 tonnes, a 33.7 percent decline from 2021. Overall fish stocks dropped 20 percent in the same period to 2.23 million tonnes.

In Kenya’s share of the lake, annual fish production has fallen drastically, nearly halving in two decades, from 200,000 tonnes in 2002 to just 98,000 tonnes in 2022.

Threat of extinctionThe International Union for Conservation of Nature (IUCN) warns that 20 percent of the 651 freshwater species native to Lake Victoria are at risk of extinction, while 76 percent of the lake’s 204 endemic species are under threat.

But scientists and conservationists warn that the rush to embrace cage aquaculture, if left unchecked, could slowly poison the very lakes and rivers on which the industry depends.

A recent review led by Edwin Baluku of Uganda’s National Environment Management Authority (Nema) describes cage aquaculture as a “double-edged sword.” On the one hand, it offers food security, jobs, and export earnings, on the other, it is driving nutrient pollution, biodiversity loss, and fuelling tensions with traditional fishing communities.

In East Africa, where population growth outpaces fish supply from capture fisheries, the shift was inevitable. Uganda’s story is emblematic. The government has actively courted investors, licensing more than 2,000 cages on Lake Victoria and Lake Albert.

Kenya, which legalised cage aquaculture in 2016, has also seen rapid uptake. By 2023, the Ministry of Agriculture estimated more than 4,000 cages on the Winam Gulf (northeastern Lake Victoria into western Kenya) alone, operated by both private entrepreneurs and community cooperatives.“It is a revolution,” says 34-year-old farmer James Odhiambo, who owns 12 cages in Homa Bay. “I used to earn irregularly from artisanal fishing. Now, I have contracts with hotels in Kisumu, and I employ six young men full time.”For many young East Africans, cage farming offers a way into agribusiness at a time when land is scarce and unemployment is high.

Read: How cage farming in Lake Victoria is boosting fish stocksExpanding marketsKenya, Uganda, and Tanzania are positioning themselves to meet rising fish demand in the Democratic Republic of Congo, South Sudan, and even Middle Eastern markets.“Cage farming is the future,” argues Uganda’s State Minister for Fisheries, Hellen Adoa. “It allows us to meet nutritional needs and create jobs without depending on dwindling wild fish.”Baluku notes that tilapia raised in cages can grow to market size in eight months, producing up to 12 times more fish per hectare than capture fisheries.“For many young people, it’s an entry point to business and income,” he says. This efficiency is critical in a region where per capita fish consumption has fallen.

The trade-offBut there is an environmental trade-off. This growth, warns Baluku, comes at a cost.

Environmental Impacts of Cage Fish Farming: A Review, co-authored by Barirega Akankwasah, executive director of Nema, and six other experts, warns of troubling signs. According to their review, published in the Open International Journal of Fisheries and Aquatic Studies, fish cages release uneaten feed, faecal matter, nitrogen, and phosphorus directly into lakes, leading to algal blooms, oxygen depletion, murky water, and fish kills.“These blooms cloud the water, deplete oxygen, and suffocate both farmed and wild fish,” the researchers say.

Farmed species escaping their cages, such as the voracious North African catfish, are also disrupting natural ecosystems, preying on native fish and competing for food, while dense stocking can fuel the spread of parasites and diseases between farmed and wild fish.“There’s a real danger of losing biodiversity. We could end up with a lake dominated by a few hardy, pollution-tolerant species,” the Buluku-led team of researchers warn.

The cages themselves are not without fault. Corrosion of their metal structures leaches copper and zinc into sediments. “There is evidence of localised dead zones around intensive cage clusters,” says Dr Edward Nyeko, an aquatic ecologist at Makerere University. “The lake cannot keep absorbing unlimited waste.”The cages also facilitate disease transmission. Parasites such as fish lice and bacterial infections spread quickly between dense stocks and wild populations, undermining both farmed yields and biodiversity.

Frosty relationsThe boom has also redrawn social relations on the water. Traditional fishermen accuse cage farmers of privatising public resources.“We are being squeezed out of our own lake,” laments 52-year-old fisher Paul Okoth from Siaya. “Cages block breeding grounds, restrict our nets, and yet we don’t share in the profits.”In Uganda, disputes have escalated into vandalism and arson, with cages set ablaze in Jinja in 2022 amid tensions between artisanal fishers and commercial operators.“Without clear zoning and conflict resolution, cage aquaculture could become another flashpoint between investors and local communities,” the review warns.

East African governments find themselves in a delicate balancing act. Uganda has introduced cage licensing, limiting density to one hectare of cages per 50 hectares of open water, though enforcement remains patchy.

Kenya, meanwhile, has attempted to regulate cage numbers in sensitive bays, but illegal, unlicensed installations remain widespread.

The Baluku review calls for urgent reforms to make cage aquaculture more sustainable, including stronger environmental monitoring and routine water quality checks to detect nutrient overload.

It also urges the introduction of zoning policies to keep cages away from ecologically sensitive areas such as breeding grounds and shallow bays, alongside better waste management practices through floating feed collectors and low-pollution feeds. In addition, the review emphasises the need for strict stocking limits to prevent the over-concentration of cages in single locations.“Cage aquaculture is not inherently bad,” notes Dr Nyeko. “It just needs governance. The same way we regulate land agriculture with fertiliser limits, we must regulate what goes into our lakes.”As the review concludes, “Cage farming is here to stay. The question is whether East Africa will manage it sustainably or repeat the mistakes of overfishing, trading short-term gain for long-term loss.”Possible scenariosExperts outline three possible futures for cage aquaculture on Lake Victoria. In the first, a “gold rush” scenario, cage numbers multiply rapidly, profits surge, but the boom eventually collapses as the lake’s ecosystem deteriorates.

The second path envisions tighter regulation that may slow short-term growth but secures long-term sustainability.

The third, more optimistic trajectory, is innovation-driven, where farmers adopt waste recycling, advanced feeds, and offshore cage systems built for deeper, more resilient waters.

For farmers like Odhiambo, the hope is that governments strike the right balance. “We want to farm fish, but we don’t want to kill the lake. This is our inheritance,” he says, gesturing to the blue expanse of Lake Victoria.

The stakes go beyond fish. East Africa’s lakes are transboundary resources underpinning multiple economies. Lake Victoria alone provides food, transport, hydropower, and tourism to over 40 million people across Kenya, Uganda, and Tanzania. For policymakers, the challenge is how to balance the industry’s economic promise with ecological responsibility.

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