Residents in South Canterbury are being assured water in the region is safe, after arsenic and DDT were found in the Opuha River.
Contaminated sediment was removed from the river yesterday after being found near Skipton Bridge.
Health officials said there was no evidence the granules had dissolved and poisoned the water, Radio New Zealand reports.
Tests will be carried out on the water quality over the next few days but Acting Detective Senior Sergeant, Richard Quested, says they are working with Environment Canterbury to reduce any risk to public.
"Police would like to reassure the public that they are working with Ecan and other agencies to ensure the risk to the public is minimised."
It is believed the poison was dumped by someone in the past few months, but Sen Sgt Quested says the investigation is in its infancy and police are appealing to the public for information.
3 News/ NZN