Chemolithotrophic bacteria found in the sediment or on particles suspended in natural waters are responsible for the oxidations of ammonia first to nitrite and then to nitrate, hydrogen sulfide oxidation to sulfate, and oxidation of ferrous iron to ferric iron. They produce the familiar whitish yellow sulfur patches on rich organic mud flats of estuaries or saline lakes and form the rust-colored gelatinous masses often found in streams.