The discovery of massive fish kills at Lake Victoria —mostly from aquaculture cages at Dunga Beach in Kisumu County—has triggered alarm across the region, exposing deepening ecological stress in Africa’s largest freshwater lake.

Massive Fish Kills at Lake Victoria: Why Oxygen Depletion Is Only Part of the Story

While initial investigations suggest oxygen depletion as the immediate cause, environmental experts and local authorities agree that the real crisis runs deeper.

Speaking after launching an emergency response, Kisumu County Executive for Livestock and Fisheries, Ken Onyango, confirmed that the county government and the Kenya Marine and Fisheries Research Institute (KMFRI) have begun joint efforts to collect and safely dispose of the fish while probing the incident’s root causes. “We are working closely with relevant agencies to establish the cause,” Onyango said.

“But in the meantime, it is crucial that no one attempts to sell the dead fish. All affected stock must be collected and buried safely.” Oxygen depletion or hypoxia—is a well-known killer in aquatic systems. It often occurs when excess organic matter, such as sewage or decomposing algae, enters water bodies, promoting algal blooms.

When these blooms collapse, the decomposition process rapidly consumes oxygen, leaving little for aquatic life.

The phenomenon is made worse by eutrophication, which results from nutrient pollution—particularly nitrogen and phosphorus—typically from agricultural runoff, untreated effluent, or sediment-laden storm water.

Environmental pressures

But environmental expert argue these environmental pressures are not new to Lake Victoria. What is new, however, is the accelerating interaction between these stressors and poorly regulated aquaculture practices.

As fish cage farming expands along the Kisumu shoreline, so are the risks. While the promise of higher yields and income has made cage aquaculture an attractive venture, the industry’s rapid growth has outpaced regulation.

According to ecological expert Lynet Ombewa, part of the recent die-off may be linked to fish farmers’ use of uncertified, highfat feeds in an attempt to speed up fish growth.

“These feeds, she warns, degrade differently in water, producing concentrated organic waste in the confined space of the cages,” Ombewa explains.

Environmental scholar Prof Raphael Kapiyo revealed that the convergence—polluted lake water from external sources, combined with poor feed practices within the cages—has created a dangerous feedback loop

“While oxygen depletion may be the final blow, the root causes lie in unmonitored aquaculture systems, weak enforcement of environmental laws,” said Prof Kapiyo.

  • By Kepher Otieno @Peopledailyke

https://farmerstrend.co.ke/wp-content/uploads/2025/09/G2FmF5SWUAA35VI.jpghttps://farmerstrend.co.ke/wp-content/uploads/2025/09/G2FmF5SWUAA35VI-150x150.jpgFarmersTrend# TrendingFish FarmingThe discovery of massive fish kills at Lake Victoria —mostly from aquaculture cages at Dunga Beach in Kisumu County—has triggered alarm across the region, exposing deepening ecological stress in Africa’s largest freshwater lake.While initial investigations suggest oxygen depletion as the immediate cause, environmental experts and local authorities agree that...New Generation Culture in Agriculture