Dog owners are being warned to keep their pets off Westport beaches after hundreds of rats washed up there yesterday.
The Department of Conservation said they may be victims of a recent 1080 drop 140km away in the Lewis Pass National Reserve.
There is a risk dogs could be poisoned if they eat the dead rats.
Doc said they may have been washed down the Buller River in recent heavy rains and deposited on beaches near the river's mouth.
Samples of the rats have been taken and sent away for testing but Doc said results could take two to three days to come through.
Doc Western South Island operations director Mark Davies said while it was possible the rats could have come from a recent 1080 drop, reports of dead fish and birds, along with the rats, were not consistent with the way 1080 was understood to work.
Signs have been posted on Westport beaches and work is now under way to remove the dead rodents.
