Human pressures strain Lake Tanganyika’s biodiversity and water quality

BUJUMBURA — The squeal of passing bikes fills the air in the center of a newly created wetland on the outskirts of Burundi’s main city and largest urban settlement on Lake Tanganyika, the resources of which the country shares with Tanzania, the Democratic Republic of Congo (DRC) and Zambia.

A step away from this landscape of houses submerged by the lake, and with palm trees shooting high into the sky, a boy stands on a perch with a fishing rod. Despite the scorching sun overhead, he slowly fills a plastic bucket with small fish.

The Lake Tanganyika sardine (Limnothrissa miodon), a fish endemic to the world’s second-oldest freshwater lake, is a welcome catch in landlocked Burundi. Known locally as kapenta, it’s an important food source for millions of people, but stocks of this and other fish species have been declining over the years. Paradoxically, the expansion of the lake’s area has not been conducive to the species’ proliferation.

Lake Tanganyika has always had its whims, flooding people’s properties occasionally. But catastrophes of any size were previously minimal, with the water receding after some time.

What has changed for Burundian people relying on the resources of the lake, and what does it say about the condition of this shared East African resource?

According to the International Organization for Migration (IOM), natural disasters have displaced around 85% of the country’s 113,000 internally displaced people, with Burundi being one of the 20 countries most vulnerable to climate change.

“We don’t have anywhere to go,” says Marie Rukuki, one of the residents of Gatumba village who decided to stay in her house near the waterfront. “The lake has been inching closer and closer for a long time, and then swallowed schools, farm fields and houses — all at once,” she says, waving toward the tall Guinea grass (Megathyrsus maximus). The grass planted itself behind the pathway of sandbags, and now obscures the view of what remains of ruined buildings.

Burundi’s growing population has also exposed the country’s vulnerability due to a shortage of land, and resources aimed at conserving the lake are lacking.

“There is no special study about the causes of recent flooding,” says Emmanuel Nshimirimana, executive director of Biraturaba (“It is our concern” in the Kirundi language), pointing to one of many research gaps on the lake.

The Burundi Ministry of Environment, Agriculture and Livestock recently visited the site of a proposed dam on the Lukuga River in the DRC, which is Lake Tanganyika’s only outlet. Experts found that the river’s bed was restricted, and recommended enlarging it order to prevent the possible further rise of water levels.

For Nshimirimana, “the reason behind the flooding remains unclear.” Solid waste and sedimentation are likely to contribute to this phenomenon, he says, giving the example of a government plan to improve the clearance of sewage solids, an initiative which remains only on paper.

Industrial and municipal sewage are not currently treated before entering the lake, possibly contributing to eutrophication, which is manifested in the appearance of large amounts of algae and invasive plant species.

“Also, it is vital to control erosion — to protect the lake from the landslides — but there are projects covering only small areas, not the whole one,” Nshimirimana says.

The primary cause of this are farmers moving into areas where tree cover has been reduced due to felling for timber or fuel. Loss of soil and soil fertility in the watershed results in an increase of sediments and nutrients being washed into the lake.

The most prevalent issues along the shoreline, as well as elsewhere in the catchment, are deforestation and erosive farming techniques. However, there are other causes of erosion, such as substandard road and related infrastructure construction and maintenance, as well as poorly placed and managed human settlements. When any of these human pressures are applied to riverbanks or steep slopes, they cause dramatic landslides that move enormous amounts of mud and soil.

Proponents say sustainable farming should become the main goal in all countries surrounding the lake. This also extends to using fertilizers and pesticides in a way that, while adding value to crop production, is also effective in soil and water conservation.

However, while in Burundi there’s only one factory that manufactures fertilizer, and it’s illegal to import it, “in some areas quantities of fertilizer used are huge,” Nshimirimana says. But without the exact data, it remains an obstacle as to how to address the problem.

Also, the authors of a strategic action plan concluded that agriculture has grown in importance in the places where fishing has declined. This, combined with population growth, has resulted in land scarcity near the lake, as farmers are forced to clear steep slopes for crops.

There have been few attempts to enhance agricultural methods, due to a lack of suitable farming traditions, and the belief that farming is still not as essential as fishing.

While annual fish catches in Lake Tanganyika have been increasing since 1970, there’s a gap in precise data, resulting from poor taxation and statistics practices. Many Burundian fishers don’t pay tax, and that makes it difficult to know how much is being caught. This data gap exists despite the lakeshore being patrolled by both civil and army personnel.

“Fishermen are in movement,” says Oscar Siyawezi, a lake authority official in the southern town of Nyanza Lac. “They go to remote places for fishing, we do not know the exact numbers of their catch. Fishing here has always been a struggle due to old-fashioned techniques,” he adds.

For the Burundian buyers, there is, however, a difference in what is now available for sale at markets compared to the past. “If we find mukeke [Lates stappersii] in the market, it is there only in small numbers,” says Sylvie Nyezi, a Nyanza Lac resident.

“Every quarter, the government enforces [a] fish ban lasting two to three weeks, but despite this, the ban is not sufficient [for fish to recover],” Nshimirimana says.

In Nyanza Lac, people dug a 20-kilometer (12-mile) trench aimed at preventing eroded soil from getting to the lake, and planted acacia trees (Acacia sensu lato) along the shore in actions led by the country’s former president, focused on raising environmental awareness.

In Burundi’s main towns, security guards work day and night shifts, checking if fishers use forbidden methods, including outlawed nets with a small mesh, electric shock fishing, or chemical attractants. But many point out that the patrols have limited impact due to the sheer size of the lake.

“Fishermen can be given the penalty of $200 or get jailed for six months if caught practicing the harmful methods of fishing,” says Jean Mumo, one of the civil security guards. Yet the nets can still be legally imported from Tanzania and the DRC, and “the fishermen using them always get a very big catch,” he adds, pointing to the policy gaps.

Hippos and crocodiles: Up or down?

Mumo recalls a hippo attack during one of the patrols that he conducted. “I am endangering my life to do this job,” he says, crediting his speed for escaping the animal unharmed.

“Only one time did I spot a killed hippo,” he says when Mongabay asked about this crime for which violators can face up to five years in jail. Stories about the population of hippos (Hippopotamus amphibius) rebounding also circulate from time to time, but many people suspect a decline in population. Lack of vegetation due to construction around the lakeshore sometimes even forces these animals to invade households, and this prompts residents to defend themselves. While these conflicts go mostly unreported, some Burundians have come up with a preventive strategy: they dig a deep trench between the vegetation and the lake, making the hippo’s climb up to the plantings almost impossible.

Similarly, data on Lake Tanganyika’s population of another freshwater species, the Nile crocodile (Crocodylus niloticus), aren’t readily available. Most often they’re seen at the mouth of the Rusizi River, but the reptiles seem to shun human attention.

Researchers have found that overexploitation of the lake poses the main threat to the crocodiles and hippos, while other dangers include dam construction and pollution. The conservation of both species and their habitats can bring significant benefits to other freshwater species, though: these two animals help to transfer nutrients from land to water, and maintain open water for the benefit of other aquatic species.

Rusizi National Park serves as nearly the last refuge in Burundi for important populations of these species, plus bushbuck (Tragelaphus scriptus) and sitatunga (Tragelaphus spekii), as well as bird and fish species. Therefore, the lake’s Strategic Action Programme states, the park should be more broadly protected, as the major threats to diversity are unlikely to be mitigated by protecting a small area of the delta. However, the park has never had an exclusion zone, so residents of nearby villages have always been able to fish its waters.

Palm oil pollution

The park and other parts of the Burundian lakeshore, from the very north to the south, are encircled by oil palm plantations that have been expanding over the past 12 years, with mainly artisanal processing units producing 80-90% of the country’s palm oil. Chemical effluent from this process pollutes the Rusizi River and is linked to declining fish stocks, a subject the authorities have recently tried to address.

The country’s Palm Oil Office has launched campaigns aimed at abandoning such practices that are harmful to the biodiversity of the lake, and promoting the conversion of palm residue into fertilizer.

Yet these are just a portion of the chemicals released into the environment by human activities that endanger aquatic ecosystems and the use of water. That means the lake’s biodiversity, water quality, and other natural resources are coming under ever greater strain.

The Belgian Development Agency, Enabel, recently launched the Lake Tanganyika Water Management (LATAWAMA) project geared toward supporting the Lake Tanganyika Authority in its mission. “As there is no monitoring system, it is difficult to make a clear identification of problems.,” says Didier Cadelli, its coordinator. The project will establish a water quality monitoring network in Burundi and neighboring countries, gathering precise data, but for now, it faces difficulties in sourcing technical experts due to budget constraints.

On the Burundian side, sampling sites will be established from the Rusizi River all the way south to Nyanza Lac, Cadelli says. With the area of the lake being so large, sampling sites will be spread widely, but can’t monitor the whole lake.

Another proposal could bring 27 million euros ($26.8 million) from the European Union to expand the project in years to come, bringing hope of increased health for the ancient lake, and sustainable livelihoods for the many people relying on its vast resources.