Lake Aha, located in the suburb of Guiyang? Guizhou Province, is a medium artificial reservoir with seasonally anoxic hypolimina. After a long-term accumulation, iron and manganese are enriched in the upper sediments. When waters of oplimnion and hypolimnion are anoxic in late summer and early autumn, Fe²⁺and Mn²⁺ formed by biological respiration, are diffused upto the overlying waters from the sediments. However, the concentration of Fez+increases later and se-creases earlier than that of Mn²⁺. Generally, sulphate reduction takes place within 6cm depth of the sediments. Whereas in the anoxic season, the reduction reaches the upper sediment, inhibiting the diffusion of Fe²⁺. Meanwhile? manganese oxidation needing molecular oxygen as catalyst, causes the violent diffusion of Mn²⁺. Because manganese can be accumulated by microorganism in natural fresh water, it is important to seek method to control manganese remobilization through manganese accumulated action.