There's an enormous lake between Rwanda and Congo, valuable both as a fishery, and because of the presence of methane below. The resources might lead to conflict between the two countries, and the makeup of the lake could also lead to a rare and massively fatal limnic eruption like what occurred at Lake Nyos in Cameroon in 1986:
We know how devastating a limnic eruption can be. On Aug. 21, 1986, the serene Lake Nyos, a crater lake in Cameroon, unleashed a silent eruption of carbon dioxide. The invisible cloud of gas spilled over the lake’s rim, descending upon nearby villages with lethal consequences. In a harrowing instant, over 1,700 lives were extinguished as the calm waters transformed into a death trap. Lake Kivu’s significant methane content makes this scenario a possibility here, too. Given the surrounding settlements, a limnic eruption on Lake Kivu could potentially claim 2 million lives. And there are fears that rather than planning for such an eventuality, the government is undertaking work that will make it more likely.