Hydrogen sulfide is a colorless gas with a rotten-egg odor. It is produced when bacteria break down plant and animal material, often in stagnant waters with low oxygen content such as bogs, swamps, or man-made lakes and reservoirs. Industrial sources of hydrogen sulfide include petroleum and natural gas extraction and refining, pulp and paper manufacturing, rayon textile production, chemical manufacturing and waste disposal. Some bacteria change calcium sulfate, the major component of wallboard, into hydrogen sulfide. If construction and demolition debris contain large quantities of wallboard, large amounts of hydrogen sulfide can be formed.
Besides bogs and swamps, other natural sources include volcanoes, hot springs, and underwater thermal vents.