Local authorities in Haikou, South China's Hainan Province said that the over 30 tons of fish found dead in a local lake died from a salinity change, dismissing public doubts about pollution.

Piles of dead fish were found floating on Hongcheng Lake in Haikou on Wednesday morning. By Wednesday afternoon, more than 30 tons of dead fish had been salvaged, but many more kept floating to the lake's surface, China News Service (CNS) reported.

The dead fish prompted widespread public questions about pollution in the lake, but a notice from Haikou's Oceanic and Fishery Bureau said the fish died of a sudden drop in salinity in the water after they swam up into the Nandu River with the ocean's tide and entered Hongcheng Lake.

The dead fish are a type of green-scaled fish that is a saltwater fish, the bureau added, explaining that the fish's blood pressure became higher than the water pressure in the freshwater lake, causing their blood vessels to rupture.

Fan Jinghu, a department head of Jinghuan City Environment Service Co in Haikou, told reporters that the company was called after some local residents tried to scoop the fish out of the lake. More than 40 sanitation workers participated in salvaging the dead fish and preventing them from entering the market and ending up in residents' kitchens, according to CNS.

A large quantity of dead fish was also found floating in Tianjin's Haihe River in August after two explosions ripped through a warehouse at the city's port where hundreds of tons of toxic chemicals were stored.

Local authorities in Tianjin said the fish also died from a salinity change as the saltwater fish swam into the river's fresh water.