An invasive weed not thought to be present in New Zealand has been found in Canterbury.
A new Ministry for Primary Industries department, Biosecurity New Zealand, confirmed great willowherb was found in the region.
Great willowherb is a flowering plant also commonly known as the hairy willowherb, or great hairy willowherb. It is a highly invasive weed in parts of North America and in Victoria, Australia, and is sometimes mistaken for a rare, endangered native herb hairy willowherb (Epilobium hirtigerum).
Biosecurity New Zealand spokesperson John Brightwell said it had been detected at five sites, which are around the lake at Pegasus township, in the Waimakariri District, and near the Kate Valley landfill, which is about 40km north of that area.
He said if any members of the public think they see the weed, they should call MPI's biosecurity hotline.
"It's extremely important that members of the public do not attempt to remove this weed on their own. They may mistake it for other, similar-looking native plants and, just as importantly, they may risk spreading the seeds."
Mr Brightwell said the weed was characterised by its aggressive growth, and there was concern it may crowd out native wetland plants.
"It can form dense stands, impeding water flow in waterways and wetlands. It may also spread to undisturbed damp areas and invade existing vegetation," he said.
Mr Brightwell said once the extent of the incursion was understood, officials would be in a better position to decide how to deal with the weed, and eradication had not been ruled out.