One night in 1986, Lake Nyos in Cameroon released massive clouds of carbon dioxide, enveloping entire villages and killing thousands.
Since then a dicey game has been played out by scientists battling to control Cameroon's 'killer' lakes.
Scientists were baffled, but they discovered that a very rare and surprising natural phenomenon had taken place.
Omer Songwe speaks to the scientists at the centre of the discovery and the few survivors.
Travelling through remote bush land, Omer reaches Lake Nyos to find that some survivors have dared to venture back to their homes, despite warnings from scientists that not enough has been done to stabilise the lake and that it could kill again.