A Beijing resident said Monday that he saw over 1,000 dead fish floating in the lake at Beihai Park, Xicheng district.

Television actor Liu Jin said that when he went to Beihai Park at 1 pm Sunday, he was shocked to see so many dead fish on the surface of the water. 

"I thought it may be air pollution that caused the death of so many fish," said Liu.

According to Liu, he went to Beihai Park about four days ago but did not see any dead fish. 

"At that time, most of the ice had melted. So I think that it may be because of the sandstorm yesterday [Saturday], which polluted the city," said Liu, who posted a picture of the dead fish on his Sina microblog Sunday afternoon. 

His post was forwarded 550 times. Many commenters expressed their concern for people's safety when Beijing's weather is so terrible, but others pointed out that the fish may have died because of a lack of oxygen during the winter.

An anonymous official with Beihai Park said that fewer than 1,000 fish had died.

She alleged that the reason is because they had been released illegally by people in so-called "mercy releases" in the autumn, and they cannot survive the harsh winter conditions.

"The cold weather started  early, and the fish which stayed in the shallow water areas are unable to swim to the deep-water areas. So they were frozen to death during winter," she said.

The official said that in the spring of 2012, fish were also found dead in the lake, but not as many as this year.

"We hope residents do not come here to release fish because they often die. We release baby fish in the lake every spring as this time of year is suitable for their survival," said the official, adding that it is hard to keep an eye out for people who come to release fish.

Qin Xiaona, director of the Capital Animal Welfare Association, said Sunday that the continuous polluted weather will have had a bad influence on water quality.

"The accumulation of the pollutants in the smog and sandstorms will pollute the water. Many winter sports on the ice also pollute the water. These pollutants may have caused the fish to die," said Qin.

Qin said she is against the practice of mercy release because it is killing rather than freeing.

"Some types of fish are not suitable for Beijing. Besides, buying fish with the intention of setting them free will encourage people to catch fish to sell for this purpose," Qin noted.

Many fish were found dying in the lakes at Shichahai after a mercy release on February 25, Radio Beijing Corporation reported. The fish died only around 30 minutes after their release, the report said.