Sulfur in the form of sulfate is considered an important nutrient element. Mineral springs are rich in sulfate and feed appreciable quantities of this compound to the watershed. Other sources of sulfate include waste material from pulp mills, steel mills, food processing operations and municipal wastes. Many bacterial obtain sulfur from sulfate for their synthesis of amino acids. How much most lakes have is largely a factor of the type of rocks the ground water comes through.
Sulfide occurs in many well water supplies and sometimes in formed in lakes or surface waters.
In distribution systems it may be formed as a result of bacterial action on organic matter under anaerobic conditions. In may also be found in waters receiving sewage or industrial wastes. Lake muds rich in sulfates produce hydrogen sulfide during periods of very low oxygen levels that result from summer stagnation. Hydrogen sulfide is a toxic substance acting as a respiratory depressant in both man and fish. At the bottom of lakes in the summer, the sulfide concentration can be quite high as there is no oxygen down there.