Oxygen deficiency killed thousands of fish earlier this month in the sea off Qinzhou City in south China's Guangxi Zhuang Autonomous Region, not radioactive contamination as previously rumored, a spokesman with the city government said Thursday.

Local fishery authorities on April 7 issued a notice advising citizens not to buy or eat dead fish found in the sea.

Tests of the water and the fish showed that oxygen deficiency due to thriving algae in the sea there killed the fish.

The water conditions were very suitable for algae growth, and the photosynthetic organisms had absorbed much of the oxygen out of the water, the spokesman said.

The situation is improving, the spokesman added.