It's August 21, 1986, in the West Central African nation of Cameroon.

It's evening and in the villages around a lake called Nios, people are getting ready to

go to sleep.

These are farming and ranching communities, and it's been a long, hard day.

But then, they hear some strange rumbling sounds, start coming from the direction of the

lake.

Others start to get headaches and say they smell something like gunpowder or a car exhaust.

They begin to feel tired and unable to keep their eyes open, and then they fall unconscious.

Hours later, some of the villagers wake up, but when they do, they discover that almost

1800 of their neighbors, their fathers, mothers, children, friends, people they know, have

all died.

Rumors spread quickly about what could have caused this disaster.

Maybe it was an attack of some sort, an explosion, poison gas.

Some say it was maybe from a bomb or a volcano.

Others have an even stranger theory that maybe it had something to do with the lake itself.

I'm Dylan Thoris, and this is Atlas Obscura.

Today, we'll hear the story of this mysterious and tragic disaster, and we'll meet two of

the scientists who did the work to figure out exactly what happened on that night of August

21st, and how to make sure it never happens again.

The story of Lake Nios, after this.

We went there when the rains had started, so it was incredibly green with all of the grass,

and then there's just this little jewel of a blue lake surrounded by these high cliffs,

...