A 1080 possum control campaign is due to begin in May covering 11,000 hectares of hill country near Upper Hutt.
Wellington Regional Council says areas around the western Hutt and eastern Hutt rivers at the southern end of the Tararua ranges, and part of the Kaitoke Regional Park and the Akatarawa saddle, are being treated.
The council says declining bird numbers show possum numbers have begun to rise for the first time since a similar operation in 2003.
Dog owners are advised to keep their pets on leads in the area during the winter. Water will not be taken from the catchment.