Lake Victoria's choking crisis: How pollution is turning Winam Gulf into a smelly crisis

Old fishing boats parked along the shores of Lake Victoria at Dunga Beach, Kisumu, where fish traders buy and sell their catch. [Rodgers Otiso, Standard]

At dawn along the shores of Kisumu, Lake Victoria no longer introduces itself with calm waves, fishing canoes or the soft reflection of sunrise across its vast waters. Instead, the lake now arrives with something far less welcoming. A smell.

Thick, persistent and sometimes suffocating, the odour rises from the Winam Gulf before the city fully wakes. It spreads across Dunga Beach, Nyamasaria, Nyalenda, Kisian and surrounding lakeside settlements, drifting into homes, fish markets, roadside eateries and even public transport stages near the shoreline.

On some mornings, residents describe it as the stench of rotten eggs. On others, it resembles sewage, decomposing vegetation or stagnant waste trapped in warm water. Whatever the description, the experience is the same; unavoidable.

Public Health Director Dr Frederick Oluoch during an interview with The Standard. [Rodgers Otiso, Standard]

For communities that depend on Lake Victoria for fishing, trade and water supply, the smell has become an unwanted companion. But scientists and environmental experts say what residents are experiencing is not just an inconvenience; it's a signal of a lake under severe ecological pressure.

Lake Victoria is Africa’s largest freshwater lake and the world’s second-largest by surface area. It is shared by Kenya, Uganda and Tanzania, supporting more than 40 million people through fishing, transport, agriculture and water supply.

Environmental scientists describe the lake’s current condition as eutrophic - a state where excessive nutrients, mainly nitrogen and phosphorus, accumulate in water bodies.

These nutrients enter the lake through multiple pathways: untreated sewage from urban settlements, agricultural runoff carrying fertilisers, industrial effluent, stormwater drainage, decaying organic matter, and invasive vegetation such as water hyacinth.

Lake Victoria in Dunga, Kisumu County. [Rodgers Otiso, Standard]

Once inside the lake, these nutrients act as fuel for uncontrolled biological growth. Algae begin to multiply rapidly, forming thick green blooms across the water surface. While this may initially appear like natural productivity, it triggers a dangerous chain reaction beneath the surface.

When the algae die, bacteria begin decomposing them. This decomposition process consumes dissolved oxygen in the water, creating oxygen-depleted zones. In these low-oxygen conditions, aquatic life struggles to survive, fish suffocate, organic matter accumulates and bacteria switch to anaerobic decomposition.

This process releases gases such as hydrogen sulphide, ammonia, methane and other volatile sulphur compounds responsible for the foul smell now increasingly associated with parts of the Winam Gulf.

Dr Christopher Aura, Director of Freshwater Systems Research at the Kenya Marine and Fisheries Research Institute (KMFRI), says the smell experienced along Lake Victoria is not random; it is a direct biochemical outcome of nutrient overload and oxygen depletion.

He explains that eutrophication has intensified due to a combination of human activity and climate stress.

“The unpleasant odour in a eutrophic lake such as Lake Victoria is primarily caused by excessive nutrient enrichment from decaying water hyacinth, agricultural runoff and urban discharges,” Dr Aura explains.

According to him, once algal blooms die, decomposition begins immediately, consuming oxygen at a very high rate.

“This leads to oxygen-depleted conditions. Under such conditions, bacteria shift from aerobic to anaerobic processes, producing hydrogen sulphide, ammonia and other volatile sulphur compounds,” he says.

He adds that warmer water temperatures, linked to climate change, accelerate the decomposition process. “When temperatures rise, biological activity increases. That means faster decay, faster oxygen consumption and stronger odours,” he explains.

Dr Aura notes that sheltered zones like the Winam Gulf are especially vulnerable due to limited water circulation.

“Areas with slow water movement trap nutrients and organic matter. That is why the smell is more intense around Kisumu’s shoreline,” he says.

For environmental conservationist Hesbone Okoth, who works with Friends of Dunga Swamp and Nature Kenya, the smell is not just a scientific outcome; it is a warning sign of a system in distress.

Standing near the Dunga shoreline, he describes a lake overwhelmed by both visible and invisible waste. “Our rivers have become dumping sites,” he says. “Everything ends up in the lake: plastics, diapers, sewage, dead animals. There is no filter anymore.”

He identifies River Kibos, River Kisian and other tributaries feeding into the Winam Gulf as major pollution channels. “These rivers carry untreated waste directly into Lake Victoria. By the time it reaches Dunga, it has already caused damage upstream,” he explains.

According to Okoth, wetlands that once acted as natural purification systems are no longer functional. “We only have one major wetland here at Dunga, and it is overwhelmed. It can no longer clean the water the way it used to,” he says.

He links the breakdown to rapid urban expansion and weak enforcement of environmental laws. “As Kisumu grows, informal settlements are rising without proper sewage systems. Waste is directed straight into drainage channels that lead to the lake,” he says.

He warns that fish breeding areas are being destroyed, threatening the long-term sustainability of the fishing industry. “When breeding grounds are polluted, fish populations collapse. That means the future of fishing is also at risk,” he adds.

Okoth insists that clean-up efforts focusing only on shorelines are not enough. “We clean the shore, but the pollution continues upstream. Unless we address the source, we are only treating symptoms,” he says.

Michael Nyaguti, Chairperson of Magnum Environmental Network, says repeated observations around the Winam Gulf suggest a more complex pollution mix involving both domestic and industrial sources.

He describes cases where fish die-offs and water discolouration appear in specific zones of the lake. “We have observed fish deaths around intake areas. Sometimes the water turns green, sometimes dark brown. That variation is not natural,” he says.

Nyaguti argues that while sewage and agricultural runoff are major contributors, industrial effluent may also be playing a role. “There are concerns that some wastewater systems may not fully treat industrial discharge before it enters municipal systems or rivers,” he says.

He emphasises that these claims require independent verification through transparent testing. “We are calling for open access to water testing points. If everything is fine, then there should be nothing to hide,” he says.

Nyaguti adds that pollution appears to intensify in cycles, often after suspected discharge events, followed by fish deaths and strong odours.

He warns that without transparency, public trust in environmental institutions will continue to decline.

The Kisumu Water and Sanitation Company (KIWASCO) has confirmed that raw water quality from Lake Victoria has deteriorated, especially from the Dunga intake point.

Engineer Moses Jura explains that climate-related changes, eutrophication and upwelling events are affecting water quality.

“In June 2026, we experienced abnormal odour due to upwelling. This brings deep lake water to the surface, which is low in oxygen and high in decomposing organic matter,” he says.

He adds that algal blooms and nutrient buildup are increasing treatment challenges. “Eutrophication has increased the load of organic matter. That means we must use more chemicals and adjust treatment processes,” Eng Jura says.

KIWASCO, however, assures residents that treated water remains safe. “We are meeting WHO and national standards. Even with raw water challenges, the final product is safe for consumption,” he says.

He notes that Kajulu water intake remains relatively stable, supplying a majority of Kisumu’s water needs.

For Kisumu County Public Health Director Dr Frederick Oluoch, the smell is more than an environmental issue; it is a public health warning. He explains that the decomposition of organic matter in oxygen-depleted water produces toxic gases.

“The gases include hydrogen sulphide and ammonia. These are responsible for the foul smell,” he says.

He adds that oxygen depletion also leads to fish deaths and ecosystem instability. “When oxygen is consumed faster than it is replenished, aquatic life suffocates,” he explains.

Despite the environmental pressure, he clarifies that properly cooked fish remain safe for consumption. “The concern is more about raw water quality for treatment plants than fish safety. Treatment systems may need adjustments because the raw water conditions are changing,” clarifies Dr Aura.

Dr Oluoch confirms that county teams are monitoring the lake and removing dead fish when necessary to reduce health risks.

He says pollution sources include untreated sewage, industrial waste and runoff from informal settlements. “Some waste enters rivers through drainage systems, especially during rainfall. From there, it ends up in the lake,” he says.

He adds that enforcement is ongoing in collaboration with NEMA and other agencies. “We are tracking discharge points, including night-time dumping activities. Enforcement is continuous,” he says.

For residents along the shoreline, the crisis is not theoretical; it is daily life.

Fish trader Eunice Otieno says the smell has changed how she works and lives. “We sit here waiting for fish, but sometimes the catch is low. The lake smells badly, and sometimes we feel sick after staying here long,” she says.

She adds that reduced fish supply has affected income and food availability. “This is our livelihood. When fish are reduced, everything becomes difficult,” she says.

Fishermen also report declining catches, longer fishing hours and increased operating costs. Landing sites such as Dunga and Usoma have seen reduced activity compared to previous years.

The Lake Victoria pollution crisis mirrors wider environmental challenges across Kenya. According to environmental data, more than 60 per cent of Kenya’s water bodies are affected by pollution.

Air pollution remains one of the most severe environmental health risks globally, responsible for an estimated 7 million deaths every year, making it a leading threat to human health and the planet’s stability.

In Kenya, the situation reflects a growing public health concern. Air pollution levels are estimated to be 3.2 times higher than WHO-recommended guidelines, with exposure shortening life expectancy by about 13 months on average nationally, according to the Air Quality Life Index. In highly affected areas such as Kisumu, residents could live up to two years longer if pollution levels met WHO standards, while Nairobi residents could gain about 1.2 additional years of life expectancy under cleaner conditions.

The State of Global Air Report indicates that in 2021 alone, air pollution contributed to more than 30,000 deaths in Kenya, accounting for roughly 8% of all deaths nationwide.

Despite ongoing interventions, policy frameworks and monitoring efforts, the smell over Lake Victoria persists. Experts agree that cleaning shorelines alone is not enough. The real solution lies upstream, where pollution originates.

It requires stronger sewage systems, industrial regulation, wetland restoration, controlled urban expansion, better agricultural practices and consistent enforcement of environmental laws.