Disaster as up-welling wipes out Lake Victoria fish stocks

Lilian Atieno, a fishmonger, prepares fish at Dunga beach on the shores of Lake Victoria in Kisumu. Picture: Reuters

Lilian Atieno, a fishmonger, prepares fish at Dunga beach on the shores of Lake Victoria in Kisumu. Picture: Reuters

Published Nov 29, 2022


Kenya News Agency reported that local scientists investigating the massive deaths of caged fish on Lake Victoria have identified the up-welling of water as the cause.

Up-welling, a natural phenomenon caused by changes in wind direction, affected currents in Lake Victoria causes the mixing of the deep waters with that from the surface of the lake, leading to massive fish die-offs, devastating the local fishing industry and thousands of people who rely on fish as a food source.

This has led to losses worth more than 1.4 billion Kenyan shillings (R194.6 million).

Dr Christopher Aura, director of freshwater systems research at the Kenya Marine and Fisheries Research Institute (KMFRI) said that up-welling results in massive oxygen deficiency in the water which was ultimately to blame for the deaths of millions of caged fish in the lake over the past month.

'“The water which is on the surface is light and has high temperatures. It is forced to move away and the water from below comes up and occupies that space. When up-welling occurs it takes about an hour or less and the fish which is confined in the cages is deprived of oxygen,” Aura said.

Although up-welling events on the lake are normal during February-March and September-October, Aura said that due to climate change, there is evidence of a slight shift in the period of when the events occur, making them unpredictable.

According to local Kenyan news, this up-welling event is the worst natural disaster to hit Lake Victoria since a similar event killed millions of Nile Perch in 2019.

Aura added that the lack of best management practices exacerbated the situation, as many of the farmers neglected proper fish stock density regulations.

To safeguard against losses in future, Aura urged cage fish farmers in the area to form Savings and Credit Co-operative Societies (Saccos) through which they can purchase water oxygen meters.

The gadgets, he said, would enable them to check oxygen levels and harvest their stocks whenever it falls below 3 mg per litre.

The farmers, he added, have also been sensitised to always look out for any suspended organic matter on the surface of the lake and at the same time observe their stock to detect any signs of struggling to breathe.

“We are advising the farmers to always look at the mouth of their fish. If it is open it means the fish is struggling to breathe,” he told Kenya News Agency.

However, the fish are fit for consumption as they died of oxygen starvation and not a poisoning event. Aura cautioned farmers to observe the quality of the fish removed from their cages before releasing it into the market for consumption.