Lake Kivu’s Deadly Secret: The Giant Gas-Filled Lake That Rwanda Turned Into a Power Plant

On May 27, 2021, the military governor of North Kivu province in the Democratic Republic of the Congo ordered about a third of Goma to leave.  The volcano above the city, Mount Nyiragongo, had erupted five days earlier, and its lava had stopped just short of town.  But the ground kept shaking, and instruments showed molten rock creeping south underneath the city.  The governor’s order named a second danger, one most people outside the region had never heard of: the magma was moving toward Lake Kivu.

Lake Kivu looks like a postcard, with fishing boats and lakeside hotels.  But deep below the surface it holds an enormous load of dissolved carbon dioxide and methane — enough, if it all came out at once, to roll a suffocating cloud over the cities of Goma and Gisenyi and the roughly two million people who live around the lake.  It is the biggest of the world’s three known “killer lakes.”  It is also, strangely, one of Rwanda’s most important power stations.

A lake with a lid

Lake Kivu sits on the border between Rwanda and Congo, in the western branch of the East African Rift, where the continent is slowly being pulled apart.  It covers about 2,700 square kilometers (1,040 square miles) and plunges to 475 meters (1,558 feet), with an average depth of about 220 meters.  Volcanoes blocked its old northern outlet about 10,000 years ago, and it now drains south toward Lake Tanganyika.

What makes Kivu dangerous is not its size but its structure.  Most lakes turn over: in winter or in windy seasons, surface water cools, sinks, and stirs the whole column, letting gases escape.  Kivu is meromictic, meaning its layers almost never mix.  Warm, salty springs feed its depths, so the deep water is heavier than the fresh water above it — even though it is slightly warmer.  Only the top few dozen meters hold oxygen.  Below about 250 meters, the water is dark, still, and loaded with gas held in solution by the weight of the water overhead.

Where all that gas comes from

Carbon dioxide seeps into the bottom of the lake from volcanic sources in the rift.  Because the layers never mix and the pressure at depth is high, the gas stays dissolved and builds up.  Microbes in the oxygen-free depths then turn some of that carbon dioxide, along with organic matter sinking from above, into methane — the main ingredient of natural gas.  Eawag, the Swiss federal water research institute that has studied Kivu for decades, estimates the deep water holds about 60 billion cubic meters of methane and 285 billion cubic meters of carbon dioxide.

Layers in the lake-bottom mud suggest that something has repeatedly wiped out much of the lake’s life, roughly every 800 to 1,000 years — possibly sudden gas releases.  Nobody knows exactly what set those events off.  In a sense Kivu is geology running an industrial process on its own, a bit like the natural uranium reactors that once ran at Oklo in Gabon — except here the product is fuel and poison at once.

How a lake can erupt

A gas-charged lake behaves like a sealed bottle of soda.  Pressure keeps the gas dissolved; open the cap and it fizzes out.  In a lake, the “cap” is the weight of the water above.  If something lifts a parcel of deep water — a landslide, an earthquake, an underwater eruption — the pressure on it drops, bubbles form, and the bubbly water becomes lighter and rises faster.  That pulls more deep water up behind it, which releases more gas, in a runaway fountain that can empty the lake’s gas store in hours.

This is not hypothetical.  On August 15, 1984, Lake Monoun in western Cameroon released a cloud of carbon dioxide that killed 37 people.  Two years later, on August 21, 1986, nearby Lake Nyos exhaled a much larger cloud that flowed down valleys and killed about 1,746 people and more than 3,000 cattle in a single night.  We told that story in detail in “The Night Lake Nyos Exhaled,” and it is the reason scientists started looking hard at Kivu.

Kivu vs. Nyos: bigger lake, more breathing room

By area, Lake Kivu is roughly 1,700 times larger than Lake Nyos, a crater lake of about 1.6 square kilometers.  Nyos sits in a sparsely settled highland; Kivu’s shores hold two big cities and dozens of towns.  Kivu’s gas is also different: Nyos was almost pure carbon dioxide, while Kivu adds methane, which is flammable.  Some researchers have worried that a volcanic disturbance could release the methane first, with fire or even explosions, and drag the carbon dioxide out behind it.

The reassuring difference is saturation.  Before 1986, Nyos was close to its limit — the water held almost all the gas it could.  Kivu is not.  At its most gas-rich depth, around 320 meters, the total gas pressure is only about half of what it would take for bubbles to form on their own.  In the early 2000s, comparing measurements with older data from 1974 suggested methane was rising about 15 percent over three decades, and some researchers warned the lake could reach saturation within this century.  In 2018, an Eawag-led team working with Rwanda’s Lake Kivu Monitoring Programme and European partners measured the gas with three independent methods.  Their 2020 paper in PLOS ONE concluded the apparent increase was mostly measurement error and that gas levels are close to a steady state.

In plain terms: Kivu is not drifting toward a spontaneous eruption.  But that is not the same as safe.  As Eawag put it, an underwater volcanic eruption could still release the gas even at concentrations far below saturation.  And Kivu sits beside one of the most active volcanoes on Earth.

The volcano on the north shore

Mount Nyiragongo rises about 20 kilometers north of Goma.  For much of the past century its summit crater has held a churning lake of molten rock.  Its lava is unusually runny.  In January 1977, the crater walls split and the lava lake drained in under an hour, sending flows down the slopes at up to 60 kilometers per hour (37 miles per hour), the fastest lava flows on record.  At least 50 people died.

On January 17, 2002, a fissure about 13 kilometers long opened on the volcano’s south flank.  Lava poured through the middle of Goma, buried the northern end of the airport runway, and ran into Lake Kivu.  About 400,000 people fled across the border into Gisenyi, and roughly 250 died.  Scientists held their breath over the lake: around a million cubic meters of lava entered the water.  Nothing happened.  Follow-up studies found that the lava’s heat stayed in the upper layers, far above the gas-rich deep water.

May 2021: magma under the city — and the lake

The 2021 eruption was stranger.  At about 6:30 p.m. on May 22, a flank of Nyiragongo broke open with almost no warning.  A 2022 study in Nature, led by Delphine Smittarello, found that the usual signs of an eruption came after the lava, not before it: the edifice seems to have ruptured first, and magma then pushed sideways into the crust.  Lava stopped on Goma’s northern outskirts, but 32 people died, many in road accidents during the panic.

Underground, a sheet of magma called a dike spread south for about 25 kilometers.  Day by day it passed beneath Goma’s airport, then under the centers of Goma and Gisenyi, and from May 27 under the northern basin of Lake Kivu, before stopping near a fault under the lake.  It lay only about 450 meters below the surface, compared with roughly 3,000 meters for the dike in 2002.  Earthquakes up to magnitude 5.3 cracked buildings.  Authorities ordered roughly 400,000 people to evacuate, and residents of Gisenyi fled east too.

The magma never broke through, and by early June the shaking eased enough for people to start returning.  But the Nature authors flagged exactly what keeps lake scientists awake: a shallow intrusion makes an eruption inside the city, or under the lake, more plausible than anyone had thought.  Nobody has studied what a real underwater eruption would do to Kivu’s layers.  The crisis also exposed a weak link: the Goma Volcano Observatory had lost its World Bank funding in 2020.  Volcanoes have a long record of reaching far past their slopes — the eruption that caused the Year Without a Summer chilled farms an ocean away — and Nyiragongo’s reach includes a lake full of gas.

Turning the threat into electricity

The same physics that makes Kivu dangerous makes its methane easy to harvest.  Pump deep water up a pipe and, as the pressure falls, the gas bubbles out by itself.  For decades a small operation fed lake gas to the boilers of the Bralirwa brewery in Gisenyi.  In the late 2000s, Rwanda ran a government pilot plant on the lake, and in 2009 it signed a concession with the U.S.-based developer ContourGlobal for a full-scale project called KivuWatt.

KivuWatt’s floating gas extraction barge is anchored about 13 kilometers off the town of Kibuye.  It draws water from roughly 300 meters down.  As that water rises, its pressure drops from about 35 bar to 2 bar in a separator, where the gas bubbles out; the raw gas is then scrubbed in four wash towers to leave cleaner methane, which travels ashore by pipeline to gas engines.  After a construction delay of about three years, the plant entered commercial operation in early 2016 at 26 megawatts.  ContourGlobal had planned to grow to 100 megawatts, but that expansion was not pursued after Rwanda revised its generation plans.

A second developer, Shema Power Lake Kivu, reached commercial operation on February 17, 2024, with a plant designed to deliver 56 megawatts to the grid.  It runs 19 large gas engines; the carbon dioxide separated from the gas is pumped back into the lake.  In a report released in May 2026, the Rwanda Development Board said lake methane supplied about 21 percent of the country’s electricity, from 82 megawatts of installed capacity: 26 from KivuWatt and 56 from Shema.  Another 100 megawatts is planned but not yet built.

The same gas that can drift out of the ground around the lake is what a cheap handheld combustible-gas sniffer such as the TopTes PT177 Natural Gas Detector picks up around a kitchen stove or a furnace: methane is methane, whether it came from a pipeline or a rift lake.

Rules to keep the lid on

Careless extraction could backfire.  Pump the degassed water back in at the wrong depth and you could weaken the very layering that keeps the gas trapped, or carry nutrients up into the sunlit surface and set off algae blooms.  So extraction on Kivu is governed by a set of Management Prescriptions drawn up by scientists with Rwanda and Congo.  Under KivuWatt’s 25-year gas concession, it must follow those rules to keep the lake stable.

Done right, extraction may also make the lake safer.  Methane dissolves far less readily than carbon dioxide, so it accounts for a large share of the gas pressure at depth; taking it out lowers how close the deep water is to forming bubbles.  Most of the carbon dioxide, though, goes back into the lake, and it is still unclear whether harvesting alone will remove the danger.  The 2020 findings carry a sobering note for energy planners too: if the gas is not being replenished quickly, Kivu’s methane is a finite store, not an endless supply.

Living with an invisible hazard

Even without an eruption, carbon dioxide already kills around the lake.  Near Goma and Gisenyi, gas seeps from the ground and pools in hollows.  Locals call these spots mazuku — “evil winds” in Swahili.  Measurements have found carbon dioxide reaching dangerous levels at night and in the early morning, when the air is calm and the heavy gas settles; livestock and children have died after wandering into them.  It is a small-scale version of what made Nyos deadly, and the same reason a basic NDIR carbon dioxide meter such as the Temtop CO2 Monitor is useful anywhere the gas can collect — we compared several in our guide to home CO2 monitors.

Life goes on in the thin upper layer.  Night fishermen chase isambaza, a small sardine that Belgian agronomist Alphonse Collart introduced from Lake Tanganyika in 1959 and that now feeds much of the shoreline.  Politics complicates everything else.  Fighting has hampered research and monitoring on the Congolese side for decades, and in early 2025 the M23 rebel movement captured Goma and then the rest of the Congolese shore.

Lake Kivu will probably never be emptied of danger the way Lake Nyos has been tamed with a few degassing pipes.  It is simply too big.  What scientists can do is keep measuring, keep extraction within the rules, and keep watching the volcano.  For now the measurements say the lake is stable, and its methane keeps a fifth of Rwanda’s lights on.  Underneath the fishing boats and the hotel terraces, the gas waits.

Gear for detecting invisible gases