Written by on November 4, 2022

A twitter post claiming that the death of fish in Lake Victoria is as a result of poisoning is false.

“If you own a fish cage in Lake Victoria, newspaper reports last week had substantial coverage of fish in those cages dying through poisoning. I was named after the Angel responsible for good news, but my Philosophy lecturer taught me there’s nothing like good news – news is news,” states the claim.

While speaking exclusively to Sky FM, Kenya Marine and Fisheries Research Institute (KMFRI) Director James Njiru said the fish had suffocated.

“In any lake, there is always what we call stratification. There is normally a layer of cold water underneath warm water that is lighter.

The colder water in most circumstances does not have enough oxygen because of pollution,” Prof Njiru explained.

He said pollution causes algal bloom, which later die and consume oxygen.

“When it rains, the two waters mix, leading to anoxic waters (depleted of oxygen). Tilapia requires large amounts of oxygen. It thrives best in 5 milligrams per liter of oxygen while Lung Fish can live in zero oxygen. But the fish that is dying most is the Nile Perch because it is not used to living in areas with low oxygen,” Prof Njiru said, adding that the Nile Perch is dying from the deep waters.

He went ahead to say that the issue is not strange as it has happened before in Lake Nakuru and Lake Naivasha. He said there is nothing the fishermen can do to avert the deaths.

“The problem emanates from upstream. Farming has introduced fertilizers. Phytoplankton are microscopic plants that multiply very fast. They also die very fast but in death they consume oxygen,” added Prof Njiru.

When we spoke to Michael Nyaguti, the chairperson at Magnam Environmental Network, which is tasked with maintaining the cleanliness of the lake, “the death of the fish is as a result of extreme weather conditions that has made the waters at the surface of the lake to be extremely hot, forcing the cold water at the bottom of the lake to rise up the surface and the hot surface water to move down the lake, a process referred to as upwelling, leading to suffocation of the fish since the water lacks oxygen,” said Nyaguti. He also said that companies around the lake have also been releasing waste materials into the lake, leading to pollution in the lake and hence making it hard for fish to survive. “The water in the lake is currently brown in color, and this is as a result of waste materials released into the lake by factories around the lake. We’ve also found out that it’s not only fish that are dying in the lake, but also other aquatic organisms such as frogs and snails,” added Nyaguti.

KMFRI Assistant Director Christopher Aura in a statement on Sunday 23rd October 2022 said the fish died from shock following movement of deoxygenated cold water currents, which replaced the top warm lake water with oxygen, a condition referred to as potted upwelling.

“Currents found their way into cages with minimal circulation, leading to shock and death of the fish,” he said.

Dr. Aura added that pollution has led to an algae coverage of 6,000 hectares while hyacinth covers 4,000 hectares in the lake.

He said extreme high temperatures facilitate fast decomposition of algae and aquatic plants.

“Our team sampled water from where factories discharge waste into the lake. We found out that the lake has been experiencing extreme cold and warm temperatures due to climate change,” he said, adding that the deoxygenated water finds its way into the cages with minimal water circulation, thereby causing fish to die.

Dr. Aura said potted upwelling is common in shallow parts of the lake, thus the need for potential fish farmers to consult relevant authorities before embarking on the practice.

We looked into this claim stating that the recent mass fish death in Lake Victoria is as a result of poisoning and found it to be false. It misleads the public.

This fact-check was produced by Sky 106.1 FM with support from Code for Africa’s PesaCheck, International Fact-Checking Network, and African Fact Checking Alliance network.

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