A 1080 poison drop on the West Coast on Friday morning has been scaled back due to health concerns.
The aerial drop covering 9000 hectares is scheduled to start near the town of Kumara at first light. The area has been reduced by about 900 hectares in a bid to prevent the poison entering waterways.
The Animal Health Board says areas near the waterways will now be covered by groundstaff.
A residents group says it will monitor the drop.