The mechanism of formation of dimethyloligosulfides in Lake Kinneret was investigated by field and laboratory studies. The process was simulated under laboratory conditions using obligate aerobic and facultative bacteria that were isolated from Lake Kinneret and fed with different types of organo- sulfur nutrients. The lysis products of Peridinium gatunense - a dinoflagellate that dominates the phytoplankton population in Lake Kinneret during the winter-spring season - are the primary source of dimethyloligosulfides. Bacterial assimilation of the aged alga or algae lysis products yields inorganic oligosulfides, which are then methylated to form the dimethyloligosulfides. All the steps of this process are carried out under oxic conditions.