NARRATOR (MARTIN SHAW): Beneath the peaceful surface of this lake lurks a monster which has the power to wipe out the millions of people who live within its reach because deep in the bottom layers the water holds a sinister secret. It’s killed before, it can kill again. Scientists are now in a race against time to stop this serial killer from striking once more. Lake Kivu in Rwanda. Two million people live and work along its shores. Shortly after these pictures were taken the volcano, Mount Nyiragongo, just 18km away, erupted.
Killer Lakes – BBC Documentary