A lake in Haikou, Hainan province, turned into a grave for seawater fish after the recent heavy rainfall brought with it a deluge of fresh water, diluting the salt content of the entire lake to dangerous levels.

People walking around Hongcheng Lake on Sunday morning found that there were dense clusters of dead fish floating on the water's surface. The lifeless bodies of the fish varied in size and species, and some had already started to decay, emitting an odor that hung heavy in the air.

A team of 30 sanitation workers sprang into action to clean up the scene.

Peng Honglian, the assistant general manager of Haikou Jinghuan Urban Environmental Service Co, said that the retrieved dead fish would be transported to a designated location for harmless disposal, preventing any possibility of the contaminated fish entering the market or further polluting the environment.

By 3 pm on Sunday, the cleanup operation was almost completed, with eight tons of dead fish having been removed from the lake.

Upon further investigation into the incident, a discovery emerged - the dead fish floating on the water's surface were not tilapia, as initially presumed, but green scale, a species of seawater fish.

Zhou Jin, director of the water department in Qiongshan district, Haikou, said the water source of Hongcheng Lake is none other than the Nandu River, whose brackish waters are home to an array of marine life. During high tide, the green scale swim upstream into the Nandu River and find their way into Hongcheng Lake through a pump station at the river's estuary. "Most of the time, the salinity of the brackish water in the Nandu River poses no discomfort to the adaptable green scale, allowing them to thrive in this unique ecosystem," he said.

However, recent bouts of heavy rainfall in Haikou have triggered a chain reaction, altering the delicate balance of salt and freshwater in Hongcheng Lake. The sudden decrease in salinity proved fatal for the green scale, leading to a mass die-off that left the lake teeming with lifeless bodies, according to Zhou.

He noted that the local government is scheduled to replenish the lake with water from the Nandu River, restoring the salt content to levels conducive to the survival of the remaining fish populations; simultaneously, water quality monitoring and testing are being conducted to assess the health of the aquatic environment and ensure the stability of the ecosystem.

In addition, the department plans to install protective columns at the water intake point, aiming at creating a barrier to prevent marine species, such as the green scale, from entering the lake.