From publisher blurb:
A fun day out on the lake boating, fishing, and swimming. Drinks on the shore with laughing friends, then retire to lakeside cabanas for a good night’s sleep. But they never wake up. During the night, the lake — the same lake that served as the backdrop for such a pleasant day — becomes a silent killer as it belches forth a deadly, invisible cloud that suffocates the revelers in their sleep.
A limnic eruption — also known as a lake overturn — is a sudden eruption of a large quantity of carbon dioxide (CO2) gas from the bottom of a lake or similar body of water. Limnic eruptions have killed thousands by asphyxiation. On our Earth, this has only happened twice in modern times, both in 1986, and both in the west African nation of Cameroon. But scientists are fearful it could happen again, at a much larger lake with a much larger resident population. The resulting disaster would result in the deaths of up to two million people.
Hazard: Limnic Eruption! explores this rare but deadly phenomenon and offers Cepheus Engine, Cepheus Deluxe, and the Original Science Fiction Roleplaying Game Referees a chance to introduce it into hir game. This short file is packed with information on the cause of a limnic eruption, a brief history, their characteristics, and game stats.
Hazard: Limnic Eruption! Hold your breath.