Lake Nyos | Atlas Obscura. Deadliest lake in the world suffocated over 1,746 people in one night. Crater lakes commonly have high levels of CO2 as they are formed by the volcanic activity happening miles beneath them. Under normal circumstances this gas is released over time as the lake water turns over. But Nyos, rather than releasing the gas, was acting as a high-pressure storage unit. On August 21, 1986, in a Limnic Eruption, the lake erupted. In Cameroon.
Lake Nyos, in West Africa: Deep in the lake bed lies a pocket of magma that has been leaking carbon dioxide. At the end of the summer of 1986, the lake became depressurized, and the carbon dioxide rushed to the surface killing more than 1,700 people in its wake. - via http://upload.wikimedia.org/