Every two weeks, a team of scientists from the Kenya Marine and Fisheries Research Institute (KMFRI) takes place in a motorboat to analyze the water of Lake Victoria, the second largest freshwater basin in the world. The lake, whose condition is deteriorating, faces many challenges: pollution, overfishing and, more recently, abnormal temperatures that contribute to suffocating it.
James Achiya, 54, a lab technician, immerses a Yellow Spring (YSI) instrument in the water of Kisumu Bay. It immediately registers a temperature of 27.9 degrees Celsius on the surface. “It’s hot,” he comments. A rarely seen extreme. Usually the temperature fluctuates between 25 and 27 degrees. “The oxygen level is very low,” he adds. More than normal. »
Kenya is hit by an unprecedented drought, and with it comes higher air temperatures. The group of researchers accuses global warming of upsetting the ecosystem of the lake. “The water at the surface becomes warmer, and the water in the lake is more stratified and thicker,” explains Fredrick Guya, a researcher specializing in environment and ecology. Warmed water absorbs less oxygen and mixes less with deeper layers of water.
Supporting photos, Fredrick Guya says that large quantities of fish have died recently, including a good number in floating breeding cages, a phenomenon that has been increasing in recent years. “It’s because of the rising waters, caused by strong winds,” he explains. The bottom water is low in oxygen and very cold, and it contains toxic elements. The water rises, and the fish suffocate and die. The growth and reproduction of fish are also disrupted due to the warmer water.
As we travel in the boat, the opaque, greenish water catches our attention. The scientist, who also measures pollution levels, explains that it is because of the large amount of nutrients from fertilizer spills from agricultural activities, poorly or untreated sewage and industrial activities. “The origin is human,” he says, in addition to pointing the finger at rampant urbanization.
This causes algae blooms which also reduce the amount of oxygen the fish depend on to survive. Water hyacinth, an invasive plant that thrives on nutrients, but whose growth is now relatively contained in the area, also monopolizes oxygen.
fewer fish
Lake Victoria is the largest inland fishing basin in the world. Nearly 50 million people depend on it on its shores in Kenya, Uganda and Tanzania. The introduction of the Nile perch in the 1950s by the British helped boost the economy of the lake, but the fish disrupted the ecosystem and wiped out dozens of native species. Victim of overfishing, it is now also endangered.
The fishermen we met notice it: they catch less fish than before. “Yesterday, we caught 14 tilapias, says Edwin Ochieng Odhiambo, 21, met early in the morning. Some days we catch nothing at all. »
Sitting in a sailing boat that moves slowly, his colleague gradually unrolls a thin net fifty meters long in the water. The two will return around noon to harvest their catch. They will then sell them on the shores of Dunga Beach, and hand over half of their earnings to their boss, who owns the boat. “Too many people are fishing, there aren’t enough fish for the number of us,” Edwin believes.
Fishermen are catching 30% less fish than before, reports Dunga Beach manager Nicholas Owiti Didi. “In the past, we could have three tonnes of fish a day. Currently, we receive less than a ton, he says. The decline has been ongoing since 2000.” Those with more financial means are therefore turning to cage farming, the number of which has exploded over the past five years. But the capacity of the lake is limited and there is overpopulation.
“We have too many cages in the area, it’s a problem,” says researcher Chrispine Nyamweya, who regularly assesses fish stocks in the lake. “One of the problems is the lack of planning, there is no control, he believes. Most of the fish farmers have placed the cages in inappropriate places, shallow and where the water is stagnant, for economic reasons. Farmed fish also compete for oxygen with fish in the wild.
The future worries him. “We have localized problems. But if it’s not contained, it will become a global problem, he argues. It is a huge lake, which somehow has several different small lakes. Some areas are immaculate. The environment is natural and undisturbed, the water is very clear with plenty of fish. But in other places, we see high levels of pollution and unsustainable fishing practices. »
Fishermen who use illegal fishing nets and catch young fish are of particular concern, as they interfere with stock renewal.
Denounced pollution
Researchers have established that the Kisat River, whose mouth is in Kisumu Bay, is contaminated by sewage from various human activities along the river. And in Kibos, north of Kisumu, residents accuse Kibos Sugar and Allied Industries, a sugar factory, of polluting the river that flows into Lake Victoria, which the company denies.
At the edge of the Kibos river, south of the factory, the chemical smell quickly takes hold of the nostrils and eyes. “When you wash in the river, your skin stings. But I have no choice, ”reports Christopher Owiro, who, like many others, has no running water at home, and who is about to wash. Jackline Auwor, who regularly comes to wash her family’s clothes in the river, like many women, confirms this. “Our body stings once the laundry is dried and worn,” she says.
Going up the river, The duty found that pipes from the factory grounds flow into the river. An opaque black liquid also escapes into the stream. Going higher, next to the sugar cane fields, the chemical smell suddenly disappears, but the water remains brownish.
Demonstrations by residents of the village have since 2019 forced the intervention of the National Environment Management Authority (NEMA), the Kenyan environmental regulatory body, on a few occasions. But all the residents met by The duty say they have seen no change. “It’s still just as polluted, drops Lilian Akoth Ouma. The factory probably gave money to the government. »
This report was financed thanks to the support of the Transat International Journalism Fund.The duty.