Lake Kivu, Congo - The blue-green waters of Congo's Lake Kivu conceal a deadly invisible mixture that could trigger a fiery disaster or be a blessing in disguise for the 2 million people who live around its shores.

Dissolved into the cold bottom waters of the lake, which straddles a part of Democratic Republic of Congo's eastern border with Rwanda, are huge amounts of highly combustible methane gas and five times as much more carbon dioxide.

Lake Kivu lies just 15 km (9 miles) from the active Nyiragongo volcano. If forced out by volcanic activity, the methane in the waters would ignite, causing massive explosions above the surface of the lake, experts say.

At the same time, a vast cloud of carbon dioxide would drift over surrounding land, smothering all life in its path and engulfing the nearby city of Goma.

"If there's ever a volcanic eruption at the level of Lake Kivu, or if there's an eruption that starts naturally in the city of Goma and spills a large quantity of lava into the lake ... the two gasses could find a way out," Mathieu Yalire of Goma's Volcanological Observatory told Reuters.

"That would be the beginning of a regional catastrophe."

Researchers recall the 1986 disaster at Cameroon's volcanic Lake Nyos, when a lethal gas cloud erupted out of its waters and killed more than 1,700 people. Similar "killer lake" gas clouds have occurred at another lake in Cameroon and also in Indonesia.

If the same were to occur in Lake Kivu, scientists say the surrounding population of around two million people would be at risk.

Although experts view this as a "worst case" scenario, they say the possibility of such an event is growing.

In 2002, an eruption of the Nyiragongo volcano sent a river of lava through the centre of Goma, the capital of North Kivu province, spilling molten rock into the lake.

Scientists say Nyiragongo is becoming more and more active, pushing up the risk factor.

"We're lucky we haven't received enough lava in the lake so far to provoke that kind of (gas) release," said Yalire.

But he added: "There's a recent study that shows that, in the last 30 years, the amount of methane has increased by 15 percent in Lake Kivu. That is a lot. And it's worrying".


But Congo's Oil Minister Lambert Mende Omalanga said the methane gas in the lake could be tapped to generate electricity, and this would also reduce the danger of a deadly gas release.

"There is an economic benefit in the industrial extraction," Mende Omalanga said.

The minister said Congo hoped to open bidding soon by foreign investors to participate in gas extraction deals.

Across the lake, neighbouring Rwanda was already finalising a project to build a plant to convert the methane into power.

In March, Congo and Rwanda agreed a joint protocol aimed at increasing cooperation in commercial gas development.

"We have enormous energy problems in the Great Lakes region," Mende Omalanga said.

"Goma alone requires 20 megawatts of electricity, and the dam we are using now is struggling to keep up," he added.

Gas-powered electricity generation would boost Congo's attempts to rebuild its shattered infrastructure after decades of mismanagement and a 1998-2003 war and accompanying humanitarian crisis that killed around four million people.

Many parts of the vast, mineral-rich former Belgian Congo have no access to electricity, and even major cities suffer from regular blackouts.

Yalire said any process that reduced the lake's lethal gas content would be welcome.

But above the lake's shimmering surface, many local inhabitants seem almost oblivious of the danger.

As the sun sets over the surrounding mountains, fisherman Paul Mulume waits to set out for another night's work.

"I spend every night on the water ... I've been doing that for 10 years," the 28-year-old said.

"But I don't trust the lake."