Water supplies to about 200,000 people in central China have been contaminated by pollution, which has turned branches of a major river system red.
At least three tributaries of the Han river - a branch of the Yangtze - have been affected.
State media reported high levels of chemicals in the water.
China is increasingly concerned about its environment. A recent ban on plastic bags has led to the country's largest bag factory shutting down.
The Xinglong, Tianguan and Dongjing rivers were all affected by the pollution, according to the state news agency Xinhua.
A chemical spill is thought be the cause, but the source has not yet been identified and an investigation has been launched.
Gao Qijin, a water company official in Xinguo, Jianli County, told Xinhua that the water in the Dongjing river had become red with large amounts of bubbles.
Mr Gao said the company had detected the pollution on Sunday and immediately stopped drawing water from the river.
People have had to use the limited alternative water supplies
About 60,000 people in Xinguo have been left without running water as a result of the incident.
They are reportedly relying on bottled water and limited underground supplies.
Xinhua reported that five schools were closed and others were unable to provide food for their students.
Zheng Jiarong, vice mayor of Qianjiang city, said water companies in five towns had been ordered to stop drawing supplies from the rivers.
Local officials have closed a gate connecting the Han river to the tributaries, and are using water from a nearby lake to flush out the pollution.
China has been struggling to deal with pollution along its waterways
China has faced problems in the past with careless or dangerous use of chemicals for industry or agriculture.
Last week a farmer in south-western Yunnan province was arrested for destroying a nearby fish farm after he spread phosphors over his fields thinking it could be a fertiliser.
On Tuesday, China's largest producer of plastic bags announced that it had been forced to close, and lay off up to 20,000 staff.
Huaqiang factory in Henan province previously produced 250,000 tonnes of plastic bags worth 2.2bn yuan ($305m;£153m) every year.
A management official told Xinhua that the company had no choice but to close, as 90% of its product were on a list of banned products drawn up by the government in a bid to rein in waste and pollution.