Alligator weed is a pest plant that takes over pastures, is toxic to stock, clogs our waterways and creates flood risk.
The Horizons Regional Council is asking for community help to report sightings of one of the world's worst weeds.
The pest plant is growing in the Mangaone Stream and the lower Manawatū catchment.
This area includes the stream area north of Colyton through Palmerston North to the Manawatū River, and down to Foxton Beach.
Horizons biosecurity programme co-ordinator for plants Craig Davey says alligator weed spreads aggressively and thrives on both water and land.
"Alligator weed can spread by water movement such as floods, eel nets and boats.
"However, it can also spread via farm machinery, soil movement, and diggers.
"Once in a waterway stem fragments can disperse and grow rapidly, destroying the environmental, recreational and aesthetic values we hold dear.
"It can also double in area size in just two months.
"We are asking the public to check boats, trailers, vehicles and equipment for fragments before travelling between water bodies to ensure the fragments are not transported to new sites.
"We also implore farmers to insist that all contractors practise good weed hygiene and clean their equipment before entering the farm.
"Make sure supplementary feed, aggregates, soil and sand brought onto the farm is weed-free."
Davey also urges duck shooters, hunters, farmers, landowners and occupiers to report any possible sightings of alligator weed to the HRC pest plant team.
"You can identify the plant by its low-growing leaves generally arranged in opposite pairs along hollow reddish horizontal stems.
"If you suspect a plant may be alligator weed, do not remove it yourself. Call the pest plant team and we will take care of it. Removing the plant yourself may result in further spreading of it.
"We also need to keep track of where this pest has been seen."
The weed was first spotted in Palmerston North during level 4 in late March 2020.
Davey said the only previously known location of the weed in the Horizons' region was the Taumarunui effluent ponds.
"This new find is very concerning."
Report sightings by emailing Craig Davey at firstname.lastname@example.org, by messaging to the Horizons social media pages, or call freephone 0508 800 800.
For more information about alligator weed: www.horizons.govt.nz/Managing-Natural-Resources/Plant-Animal-Pests/Alligator-Weed