Waikato Regional Council says one of the world's worst weeds has been discovered at a beach in Raglan.
Alligator weed can block waterways and create problems on farms and wetlands.
It was spotted at Ruapuke Beach and the council says it may have been spread via contaminated finishing nets.
The council says it will eradicate the weed, but wants the public to keep a look out for any other signs of it.
It says Alligator weed grows very quickly and is difficult to remove, particularly if it becomes established on land.