An ethanol factory has been ordered to suspend operations after its untreated water allegedly combined with rainwater to flood over 600 homes in Suphan Buri.
A downpour on Sunday night appears to have contributed to the collapse of the water treatment pond at the factory, officials said.
The province has declared tambon Nong Makamong a disaster area after it was affected by the polluted flood water in Dan Chang district.
The Thai Agro Energy Co factory, the alleged source of the tainted water, has been shuttered for 45 days by the provincial office, according to deputy provincial governor Phipob Boontham.
The water reportedly flowed into and flooded the tambon's Sabua Kam community on Sunday night.
Mr Phipob said he met with CEO Somchai Lovisuth, representatives of affected residents and the tambon administrative organisation to discuss damage control measures and ways of urgently assisting local people.
The damage was being assessed and related laws studied ahead of possible moves to prosecute those responsible, the deputy governor said.
A centre has also been opened in the tambon to assist affected residents.
Environment Office Region 5 has dispatched officials to survey a leakage of the untreated water and the direction of the water flow. They have also taken samples for lab tests.
The Pollution Control Department (PCD) has warned residents to avoid using water from natural sources near the flooded community. Although rainwater may dilute the level of pollution, it can still irritate the skin and cause other problems.
Downstream residents in Doembang Nangbuat district were told to stay alert as the tainted water was flowing their way.
The department said it was seeking measures to stem the flow and stop it from draining into the Tha Chin River, which could do more harm to the environment.
PCD chief Sunee Piyapanpong said water samples have been collected from natural waterways for testing. She expected the results for certain contaminants would be available by today.
No charges have been pressed against the factory's management, she said. The power to seek legal charges rests with the Department of Industrial Works.
Complaints by Sabua Kam residents have piled up online, with photos attesting to their claims of "putrid" water flooding their homes and farms.
"The water looks really dreadful. I don't know if it's poisonous," read one online post.