Lake Victoria is by area (69 thousand square kilometers, 185 times the size of Lake Garda) the largest in Africa, the second largest body of fresh water in the world, after the North American Lake Superior.

The explorer John Hanning Speke, the first European to see the lake - called Nyanza by the inhabitants, but renamed by him in 1858, in honor of the sovereign of the British Empire - exclaimed, at the sight of it, that he thought he was in front of a 'tropical sea'. It constitutes the main reservoir of the White Nile. It is particularly rich in biodiversity, with its 500-600 species of fish, second in the world only to Lake Malawi. It is also the chimpanzee sanctuary on Ngamba Island in Ugandan waters. The shores of the Ssese Islands and those of the Ugandan coast are home to impressive Nile crocodiles and hippos. The island of Mfangano, in Kenyan waters, is known for its site of cave paintings dating back perhaps 4,000 years. No fewer than 230 bird species are recorded, including the famous crowned crane, Uganda's emblem.

Fish slaughter

There are, however, many threats to this fascinating universe. The first is the overexploitation of fish resources. Since the 1960s, when the Nile perch (Lates nicotilus) was artificially introduced, the balance of the ecosystem has been upset. Smaller fish have been decimated by this voracious predator that can measure two meters and weigh up to two quintals. In addition, the pressure of the fishing industry on the environment has become unbearable: the volume of fish caught has increased tenfold in fifty years to the current one million tons per year (of which about half are dagaa, freshwater sardines, and 230,000 tons of perch).

This is four times more than sustainable exploitation, estimated at 250,000 tons by Richard Ogutu-Ohwayo, professor at Uganda's National Fisheries Resource Research Institute. From 2000 to 2020, the number of fishermen tripled from 70,000 to 210,000.

According to studies by the Department of Fisheries and Aquatic Sciences of the University of Kenya as well as the Ugandan Lake Victoria Fisheries Organization (Lvfo), this abnormal exploitation is at the expense of other fish populations in the lake, including tilapias and cichlids, whose decline is accelerated by the predatory behavior of the carnivorous Nile perch. Scientists have counted two hundred different fish species there: half as many as existed in the last century. Confirmation also comes from an FAO study, which noted an alarming 41% drop in dagaa from 1.29 million tons to 700,000 in the period between 2015-20, which also went hand in hand with a 9.5% drop in the Nile perch stock, itself a victim of overfishing and in particular illegal fry fishing.

Pest plants

Other factors also intervene to explain the decline in fish stocks. In 2008, a group of researchers from the universities of Bergen (Norway), Waterloo (Canada), Wageningen (Netherlands) and Minnesota (USA) as well as the Lvfo showed how the eutrophication of the lake's waters, caused by fertilizer spillage, had a more disastrous effect on the state of the fish resource than overfishing itself. The phenomenon, in fact, encourages the development of water hyacinths (Eichhornia crassipes) a weed that has colonized the lake and now threatens to suffocate it. Photos taken by satellites show an ever-widening silt carpet. Beneath the water surface lies a murky forest of deep, branching roots. A veritable wall of vegetation, sometimes, many kilometers long, which strangles all other forms of life, traps sediment, slows down currents and hampers navigation. The spread of hyacinths and the impoverishment of the lake's biodiversity worry the Kenyan authorities, who encourage the alternative of aquaculture. Fishermen from the Dunga Beach Management Unit (Dunga Bmu) raise tilapias in cages in the lake. But it is a method that carries the potential danger of pollution due to the droppings of cage-farmed animals and the discarding of dead fish. This practice is banned in Lake Michigan, USA, where Senator Rick Jones denounced the fact that a farm of 200,000 fish produces as much waste as a city of 65,000 inhabitants.

Mercury and crude oil

The second scourge threatening the life of the lake is pollution, the population of its shores having increased tenfold since the 1930s to 40 million today. Pollution endangers fish populations because of the lack of water purification plants, complains Richard Abila, a researcher at the Kenya Marine and Fisheries Institute.

Pollution comes not only from fertilizers, but also from pesticides, herbicides and plastic bags. One of the most dangerous sources of pollution is mercury, used by gold diggers in the Olini area of Kenya, not far from the Tanzanian border, which ends up in the lake carried there by waterways. 'If action is not taken now, in fifty years Lake Victoria will be dead, with all that we pour into it,' warns Peter Nyong'o, the governor of Kenya's Kisumu County.

To all this is added the specter of an oil spill. The threat comes from a 1,445-kilometre-long oil pipeline between the fields in Uganda's Lake Albert region and the Tanzanian port of Tanga, which is being built by a consortium including the French multinational Total, the Irish company Tullow Oil and the Chinese company Cnooc. The pipeline, with a capacity of 200,000 barrels/day, is to cross the Lake Victoria basin for 460 kilometers, running alongside it for several hundred kilometers. It will be a buried pipeline. This worries many environmental NGOs as well as Oxfam International, which accuse Total of choosing the cheaper and less safe method of construction.

An oil spill would be a catastrophe for the lake's fauna and the feeding of its inhabitants, as well as for the water supply, whether to irrigate agricultural areas or to supply drinking water to the Ugandan capital, Kampala, and the lakeside towns of Kisumu (Kenya) and Mwanza (Tanzania).

In August 2019, the Tanzanian government also announced plans to build a 135-kilometre-long aqueduct with a capacity of 19,000 cubic meters to distribute drinking water to 236,000 people in 136 villages in the north of the country.

Sands and water at risk

The illegal exploitation of coastal sands for the needs of construction companies causes their depletion and degrades the ecosystem, especially along the Ugandan coast. It also leads to changes in the speed of currents, causing accelerated erosion along the White Nile, downstream, as well as deposits of sediment and disturbances to the development of aquatic flora, which, by reducing light penetration, diminish fish breeding opportunities.

Climate change is the ultimate threat to the lake, its fauna, flora and inhabitants. It is an established fact that the temperature in the region will rise between 1 and 5°C over the next hundred years. Evaporation will increase proportionally,' warns Emily J. Beverly, a researcher at the Department of Earth and Atmospheric Sciences at the University of Houston, with the risk of lowering the lake level, especially if there is a simultaneous decrease in precipitation.

The worst-case scenario indicates that within a decade or so the lake could stop flowing into the White Nile, the only way out for its waters. The consequences would be devastating for the countries downstream, as Lake Victoria is the Nile's largest supplier of water outside the rainy season on the Ethiopian highlands between July and October. The large Jinja hydroelectric dam, located at the source of the White Nile in Uganda, would no longer be fed. These predictions are based on extrapolations from the observation that the lake has already emptied completely at least twice, 17,000 and 15,000 years ago.

See L’agonia del Lago Vittori