Seven chemical company officials have been detained over industrial waste that polluted a river in the Guangxi region, China.
Cadmium pollutants were detected in the Longjiang River on 15 January after tests were carried out on dead fish.
Regional environment protection official Feng Zhennian said the level then was 80 times the official limit.
Teams have been putting neutralising chemicals into the river to treat the contamination.
Mr Feng did not name the seven people at a press briefing on Monday.
But he said one of the companies involved was Jinchengjiang Hongquan Lithopone Material in Hechi city.
The Xinhua news agency reported last week that another company, the Guangxi Jinhe Mining Co, was suspected of causing the contamination.
Officials said on Saturday that cadmium levels at the source of the pollution near the Lalang reservoir had normalised.
Mr Feng said the pollution concern was now near the Luodong hydropower station downstream. Cadmium levels there were still 25 times higher than the official limit, he added.