Growing up on the shores of Lake Kivu in eastern Democratic Republic of Congo (DRC), Kevin and his friends were often warned not to play in the water.

"My mother always asked us not to dip things like keys, rings or any metallic object in the lake," he said. "She said the metals would react with some gas and could result in an explosion."

Kevin may not have believed her at the time, but his mother’s concerns echo something scientists have been studying for a number of years – the levels of dissolved gases in the lake and whether they are a cause for concern.

Lake Kivu is one of Africa's Great Lakes, on the border of the DRC and Rwanda. It is a source of water, fish and sand for two million people and provides a vital link between the ports of Goma and Bukavu in DRC and Gisenyi, Kibuye and Cyangugu in Rwanda.

The lake is 1,460m above sea level and empties into the River Ruzizi, which flows southwards into Lake Tanganyika, covering 2,700sqkm in a volcanically active area.

Gaseous increase

Prof Boniface Kaningini, director-general of the university college Institut Superieur Pedagogique de Bukavu (ISO-Bukavu) and a biologist with at least 20 years of research on Lake Kivu, says studies show the amount of methane gas and carbon dioxide in the bottom of Lake Kivu has increased by 30 percent in the last 30 years.

Despite the existence of studies that link the increase of these gases to volcanic activity, Kaningini says another factor could be the introduction of the sardine Limnothrissa miodon – locally known as Ndakala – into the lake.

"The origin of the methane gas on the lake goes back 40 years ago when this fish was introduced into Lake Kivu from Lake Tanganyika," he said.

Since then, Kaningini says, fishermen on the lake have noticed a gradual fluctuation in the catch of fish.

A number of different studies have been taking place to examine these changes, Kaningini said.

The Swiss Federal Institute of Aquatic Science and Technology (Eawag) concluded that the "the introduction of Limnothrissa miodon, the first pelagic and planktivore fish in Lake Kivu, could be responsible for significant changes in the nutrient fluxes".

Possible dangers

Eawag’s report also said the density and layers of the water function as a flexible lid, trapping gases from the Earth’s mantle as well as gases generated in the sediments beneath the lake.

According to lake water experts, the Salmon Enhancement and Habitat Advisory Board (SEHAB), a potentially catastrophic event called a ‘limnic eruption’ could occur if volcanic or landslide activity caused the lake waters to turn over and effectively lift this ‘lid’.

A cloud of released gases would smother all lakeside life. "The only two known and observed ‘limnic eruptions’ are at Lake Monoun in Cameroon in 1984, killing 37 people; and more catastrophically in 1986, nearby Lake Nyos. At Lake Nyos, over 80 million cubic metres of carbon dioxide were released from the lake depths into the atmosphere," A 2006 SEHAB study states.

Lake Kivu, Lake Nyos and Lake Monoun are termed as "Africa's Killer Lakes" in a 2006 UN Environmental Programme (UNEP) report. It said Lake Kivu remains a cause for "serious concern" as approximately two million people live in the lake basin.

"A rift in the area is pulling apart and causing a crack to move closer to the bottom of the lake. Large amounts of boiling lava entering the lake could be more than sufficient to trigger a large overturn releasing huge amounts of deadly carbon dioxide," it said. "In addition, the lake contains a large quantity of methane that could also cause explosions above the lake."

Volcanic activity

In 2003, there was an eruption of Mt Nyiragongo near the capital of North Kivu Province, Goma.

However, Pascal Isumbisho, a biologist whose PhD thesis is on the Zooplankton Ecology of Lake Kivu, says there is no direct proof of a link between the increase in methane gas and volcanic activity.

Isumbisho, who heads the biology department at ISP-Bukavu, said: "The question is: could what happened in a lake in Cameroon [Lake Nyos] 20 years ago repeat itself here in Kivu?"

Kaningini says the risk of another Lake Nyos is minimal and so far gas levels have only affected the numbers of fish caught, not the quality.

"I would say people living around the lake need not worry; what we need to do is to conduct more research and collaborate better with the Ministry of Environment as well as with other stakeholders to understand this phenomenon," he said.

Exploiting the gas

Whatever the source of the methane, scientists agree the solution is to tap the gas as an energy source rather than risk a possible disaster.

Salif Diop, a senior programme officer and head of the Ecosystems Section of UNEP’s Division of Early Warning and Assessment (DEWA) says degassing the lake – as is being done for Lake Nyos – is a viable and economically beneficial option.

Research has shown the lake's deep waters contain an estimated 65 billion cubic metres of methane, the equivalent of 50 million tonnes of petrol.

UNEP estimates say Kivu contains enough methane to power the United States for a month, and five times as much carbon dioxide – about 200 km3.

In 2003, New Scientist reported that this reserve could supply Rwanda’s energy needs for 400 years, eliminating the need for wood burning, the main source of energy at the time.

Beer factory Bralirwa has already realised the potential and has been extracting methane gas from the lake for harnessing gas and electricity since the 1980s.

Now, says Diop, "Riparian countries of the lake should investigate necessary resources in order to make the degassing of Lake Kivu a reality".