Around 35 tons of dead fish have washed ashore on Hainan Island in China, as bodies covered vast areas of Hongcheng Lake. Biologists are struggling to understand what may have wiped out the vast population of marine animals.

One possible explanation is the creatures may have been killed as they passed through the pumping system used on the lake. The animals may have been carried in an estuary by a tidal surge of water. They would have then entered a pumping system before being deposited back into the lake. Dead fish then floated to the surface of the water over the course of the next two days.

"Massive dead fish found in lake in S. #China's #Hainan Wed for uncertain reason; workers clear over 20 tons in 5 hrs," People's Daily tweeted.

The deceased yellow and white fish are members of the herring family. They normally live in salt water, and any unfortunate specimens which found themselves in freshwater would quickly perish as water rushed into their bodies, rupturing blood vessels.

Dozens of sanitation workers were called in during an effort to clean up the mess from the mass death. Bodies of the marine animals were burned, in an effort to prevent the fish from being sold as food.

"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," The Global Times reported from China.

Hainan Island is the southernmost, and smallest, province in China. The island makes up the main part of the region, located on the South China Sea. The province is home to 10 counties, as well as the same number of major cities.

Despite the official hypothesis of how these creatures perished, some observers believe pollution may have been to blame for the recent event. A similar mass death occurred in August 2015 at Tianjin Port. The cause of those deaths was found to be a pair of explosions at a chemical plant which released cyanide into local waterways.

While some of the fish remains from this latest die-off will be incinerated, part of the population will be sent to landfills.

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