Testing of a South Canterbury river which supplies water to Timaru has come back clear of arsenic and DDT.
The Canterbury Regional Council noticed white flakes on the nearby Opuha River's bank when sediment samples were taken in August.
Test results showed the flakes contained high levels of arsenic and DDT and, as a result, the Timaru District Council stopped taking water from the Opihi River, which runs from the Opuha.
The flakes, which the Canterbury Regional Council said it believed were dumped in the river in the last month, were removed from the river bank last week.
Timaru District Council drainage and water manager Grant Hall said further testing of the Opihi River had come back clear.
"The council stopped taking water from the river three weeks ago when first alerted to the possibility of contamination," he said.
"Now we are sure the water is free from pesticides, we have started to take water for the town's supply."
The Canterbury Regional Council is still conducting tests on the Opuha River to make sure the contamination has not spread.
The regional council's water science manager, Tim Davie, said those results should be ready in another two weeks.
"We've got several fish from Fish and Game from the Opuha Lake and Opuha River which have been sent in for testing at an independent lab."
What is DDT?
Dichlorodiphenyltrichloroethane (DDT) is a pesticide. With high levels of exposure, over a long time, DDT can cause birth defects, fertility problems, greater susceptibility to disease and some types of cancers. The use of DDT in New Zealand was phased out in the 1960s and 1970s.