Source: International Atomic Energy Agency (IAEA) –
Tareq Aldakheelallah, IAEA Department of Technical Cooperation
Lake Tanganika is shared by Burundi, the Democratic Republic of the Congo, Tanzania and Zambia. (Photo: Adobe Stock)
Along the shores of Lake Tanganyika, rising waters are disrupting economic activity and daily life. The lake is shared by Burundi, the Democratic Republic of the Congo, Tanzania and Zambia. During the past five years, its water levels have increased by more than a metre. Beaches have closed and some areas with lakeside housing and cabins are now fully submerged and have been evacuated. Roads and hotels along the shoreline have also been affected.
Scientists in Burundi Working with IAEA
While these impacts are visible on land, the processes beneath the surface are less clear. With support from the IAEA’s technical cooperation programme, scientists from Burundi are working with IAEA experts to better understand changes in the lake’s water conditions using isotope hydrology.
This effort echoes a pioneering 1973 expedition, when Harmon Craig and colleagues from the Scripps Institution of Oceanography, in collaboration with the Food and Agriculture Organization (FAO), worked with national institutions including the Burundi Fisheries Department, first studied the lake’s chemistry and circulation. More than 50 years later, nuclear scientists have returned to help explain how the lake is changing.
Rising water levels have affected roads along the shores of Lake Tanganyika, impacting transport and local communities. (Photo: IAEA)
Lake Tanganyika is the longest freshwater lake on Earth and the second largest lake in the world by volume and depth. It is shared by Burundi, the Democratic Republic of the Congo, Tanzania and Zambia and supports fisheries, agriculture, transport and tourism across the region.
“Lake Tanganyika is not only important for Burundi. It is shared with three other countries. Its water management is essential, as it has long been a source of fish, drinking water and recreation for communities along its shores,” said Gilbert Nijimbere, Professor at the University of Burundi.
What is Isotope Hydrology?
Isotope hydrology is a nuclear technique that uncovers how water moves through the land, ocean and atmosphere. This technique provides data to facilitate informed decision making to address water management challenges.
Read more: What is Isotope Hydrology?
The IAEA-supported mission in February this year brought together two IAEA experts, two international specialists and two scientists from the University of Burundi. Over the course of the expedition, the team collected around 160 water samples from different lake depths, as well as from nearby rivers and groundwater sources.
Experts in Burundi are using isotope-based tracing techniques to better understand how water circulates within Lake Tanganyika, how its layers interact and how conditions may be changing over time. Some of these methods also help determine how long deep waters have remained isolated from the surface.
The measurements from the landmark 1973 scientific expedition provide an important scientific baseline for understanding how the lake has changed over the past half century.
“It’s very exciting to have the opportunity to reapply the isotopic techniques used in 1973 to examine how conditions in the lake may have changed over time,” said Bradley McGuire, an isotope hydrologist joining the 2026 mission from the IAEA.
IAEA experts and scientists from the University of Burundi collect water samples from Lake Tanganyika as part of efforts to understand changes in the lake’s conditions. (Photo: IAEA)
Deepest Waters of Lake Tanganyika 2000 Years Old
In 1973, Craig’s team collected hundreds of water samples from different depths and locations across the northern part of the lake. Their research found that Lake Tanganyika is organized in distinct layers.
The upper layers of the lake, influenced by wind and seasonal changes, were observed to mix down to a depth of roughly 100 metres, providing a connection to the atmosphere and introducing oxygen which supports larger biological life. Below this mixing zone, however, deeper layers of the lake appeared isolated. Oxygen was absent and water was believed to remain undisturbed for long periods of time.
In fact, scientists estimated that some of the deepest water was much older than the lake’s surface water, mirroring the age of deep ocean water around 2000 years, and effectively preserving a record of past environmental and climatic conditions. This layered structure means Lake Tanganyika behaves more like a miniature ocean than a typical lake.
Scientists have compared Lake Tanganyika to a miniature ocean, as its waters are thousands of years old. (Photo: IAEA).
New Measurements Reveal Depths of Oxygenated Waters Have Decreased
Preliminary observations indicate that the depth of oxygenated waters has decreased significantly compared with measurements taken in 1973. At that time oxygen extended to about 100 metres, while new measurements suggest that oxygen now reaches only around 80 metres, indicating potential changes in mixing processes and ecological conditions within the lake.
Researchers also observed that the water area between 50 metres and 80 metres appears to be a zone of oxygen stress, where oxygen levels are almost half of the oxygenated zone .
The expedition required careful coordination, including alignment with historic sampling locations, verifying equipment, and ensuring consistency with earlier measurements. Despite these challenges, the team was able to gather enough samples for detailed laboratory analysis.