The lake which killed more than 1,700 people in a single night and none of them drowned.
There is an extremely rare natural phenomenon called a limnic eruption, where a huge amount of dissolved carbon dioxide suddenly escapes from deep inside a lake.
And that is exactly what happened at Lake Nyos in Cameroon on August 21, 1986.
A massive cloud of CO2 escaped from the lake and spread into the surrounding area, killing more than 1,700 people and around 3,500 livestock overnight.
And the scary part? The gas was basically invisible and odorless.
Lake Nyos is a volcanic lake, and magma deep underground continuously releases CO2, which can gradually build up in the water.
Scientists believe some kind of disturbance caused water layers to rise, allowing the CO2 to suddenly escape, similar to what happens when you open a bottle of soda that has been shaken.
Because CO2 is heavier than normal air, the gas cloud stayed close to the ground and spread into nearby villages, where people were caught completely unaware.
After the disaster, scientists installed degassing pipes in the lake to slowly release the trapped CO2 before it can build up to dangerous levels. The system has been working and no similar disaster has happened there since.
But just imagine living next to a lake that looks completely peaceful while potentially containing enough invisible gas to kill you.
And you wouldn't even need to touch the water.
Scary, right?