A net lifts up dead fish found in the Fuhe River in central China's Hubei province after an ammonia leak from a nearby factory.

A net lifts up dead fish found in the Fu River in central China's Hubei province after an ammonia leak from a nearby factory. Photo: AP

Wuhan, China: Thousands of dead fish floating along a 30-kilometre stretch of a river in Hubei province in Central China were killed by pollutants emitted by a local chemical plant, provincial environmental officials said.

Environmental protection officials said tests on water taken from the Fu River upstream from the metropolis of Wuhan revealed that extremely high levels of ammonia in the water were caused by pollution from a plant owned by the Hubei Shuanghuan Science and Technology Company.

Tests conducted by environmental protection officials from Xiaogan City revealed ammonia concentrations in the river waters downstream from the plant were as high as 196 milligrams per litre. The World Health Organisation notes that naturally occurring ammonia concentrations in surface water are about 12 mg/l, while the guideline for drinking water is that it contains about 0.02 mg/l.

Dead fish float on the water in the Fuhe River in central China's Hubei province. Authorities scooped up about 100,000 kilograms of dead fish poisoned by ammonia from a chemical plant.

Dead fish float on the water in the Fu River in central China's Hubei province. Authorities scooped up about 100,000 kilograms of dead fish poisoned by ammonia from a chemical plant. Photo: AP

Shares in Hubei Shuanghuan were suspended from trading on the Shenzhen stock market Wednesday pending the release of an announcement. Calls to the company's headquarters were not answered Wednesday. Provincial officials ordered the company's plant to cease production while the cause of the leak is investigated.

The plant produces sodium carbonate, used in making glass, and ammonium chloride for fertiliser, according to local media reports. It has been cited for environmental violations four times since 2008, said Ma Jun, director of the Institute of Public and Environmental Affairs, a Chinese nongovernmental organisation that tracks air and water pollution.

"Each time it was ordered to be corrected, but this demonstrates that enforcement is way too weak and the cost of violations way too low," Mr Ma said.

A man removes dead fish found in the Fuhe river in central China's Hubei province.

A man removes dead fish found in the Fu river in central China's Hubei province. Photo: AP

People living along the river said they first noticed fish dying on Monday morning, and a sickening stench began to fill the air, China National Radio reported. About 110 tonnes of dead fish have been cleared from the river, the state-run Xinhua News Service reported.

Environmental officials said the river is not used as a source of drinking water, and they urged residents not to panic. Spills in China have often triggered runs on bottled water due to fears of contaminated supplies.

China's Ministry of Environmental Protection said water pollution is a serious concern, with industrial spills, farm runoff and untreated sewage all factors in degrading water quality. As of last year nearly a third of the sections of major rivers it monitored were so degraded that the water was unfit for human contact, the ministry said in its annual State of Environmental Quality report released in June.

Workers clean up dead fish on the banks of the polluted Fuhe river in Wuhan, Hubei province.

Workers clean up dead fish on the banks of the polluted Fu river in Wuhan, Hubei province. Photo: Reuters

The Fu River flows into the Yangtze, China's longest river and the source of drinking water for millions. Spills into the Yangtze and its tributaries remain a continuing problem despite huge investments in reducing pollution, Mr Ma said.

"Even though it has a large volume of water, with 40 per cent of China's wastewater dumped into this watershed we are concerned about the health of this river and the quality of its water," he said.

New York Times