The mass deaths of fish in Lake Victoria is due to massive pollution and lack of oxygen, an expert has explained.
Panicked fishermen were recently baffled to find thousands of dead fish beached on the shoreline.
But residents have been assured the dead fish are not harmful.
Kenya Marine and Fisheries Research Institute (Kemfri) 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 on oxygen). Tilapia requires large amounts of oxygen. It thrives best in 5 milligrams per litre 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.
The expert said 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 fertilisers. Phytoplankton are microscopic plants that multiply very fast. They also die very fast but in death they consumes oxygen," added Prof Njiru.
Safe to eat
"The dead fish are safe to eat, they are not harmful. They did not die as a result of poisoning. They have all the nutrients," said Prof Njiru.
In Uganda, the authorities have also ruled out poisoning following preliminary investigations into the deaths reported in lakes Victoria and Kyoga and in River Nile. Instead, the deaths were blamed on upwelling.
It was suspected that the recent storms on the lakes caused mixing of the different waters -- thereby reducing the oxygen levels in the lake.
Mixing of water
Lake upwelling is the movement of poorly oxygenated water from the bottom to the top. The process causes mixing of water resulting in the suffocation of fish due lack of oxygen.
Agriculture, Livestock and Fisheries Cabinet Secretary Peter Munya said Lake Victoria faces overfishing and pollution.
"The biggest problem in Lake Victoria is actually pollution and overfishing. But we have controlled it by destroying inappropriate fishing nets. We are guarding the area as we work on restocking. We want sustainable use of our water resources and fish," said Mr Munya told Nation.