Deep sea vents (hydrothermal vents) are fissures in volcanically active areas of the seafloor where heat and minerals escape from the earth. These vents may be a crack or, overtime with the deposit of minerals, may have built into a column that continues to spout heated mineral-enriched water from its tip. Deep sea vents are a unique underwater biome because they offer both heat and bacteria-rich water in an otherwise cold and barren deep-sea environment. They are often an oasis of strange life.

In fictional worlds, deep sea vents may pose a terrain hazard during recovery of a shipwreck, may be the territory of a great leviathan (or the place it keeps its eggs), or an important source of heat or power for underwater civilizations.

Active hydrothermal vents are thought to be present on Europa, a moon of Jupiter, as well as Enceladus, a moon of Saturn.

Water from the vents can range in temperature from 60 – 464 °C or 140 – 867 °F