Dead fish are cleared from the Fuhe river in Wuhan, in central China’s Hubei province on September 3, 2013 after large amounts of dead fish began to be surface early the day before. According to local media, about 30 thousand kilograms of dead fish had been cleared by late September 2. The official Wuhan municipal government’s emergency office Weibo account announced on September 3 that the fish had died of severely high levels of ammonia. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)

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(CNN) — At least 35 tons of dead fish appeared in a lake in southern China, leaving residents stunned.

The piles of fish washed up in a lake in Hainan province on Wednesday, Chinese state media reported.

Residents expressed concerns on pollution, but local authorities said the fish died as a result of salinity change.

The change in salinity levels likely occurred after a tide pushed the fish up farther into Hongcheng Lake in the city of Haikou, state-run People’s Daily reported.

Regional environment officials are still investigating.

It’s unclear what kind of fish it was, according to People’s Daily. It described it as the size of a half palm, saying residents had not seen that type of fish at the lake before

Dozens of sanitation employees worked for hours to trash the fish, to prevent it from being sold to consumers.

Massive dead fish found in lake in S. #China’s #Hainan Wed for uncertain reason; workers clear over 20 tons in 5 hrs pic.twitter.com/PKTScmoysr — People's Daily, China (@PDChina) May 4, 2016