World’s “Worst” Weed Found Near Thames

Alligator weed has been located at Rhodes Park Thames, and other land either side of Ngati Maru (State) Highway between Totara and the township.  Alligator weed is one of the world’s worst weeds.

alligator weed

This fast-growing weed can grow both on land and in water, where it forms floating mats. It can also tolerate certain amounts of sea water when growing in flowing water, so it’s a threat to the lower Firth of Thames, rivers and wetlands as well as land.

Alligator weed threatens farms, market gardens and urban properties. It clogs waterways and drains, increasing sedimentation and flooding risk. Access to waterways for recreational purposes (boating, fishing) can be blocked and plants may affect whitebait spawning areas. Alligator weed spreads aggressively from even the smallest stem fragments. It can double in area in less than two months. It can out-compete pastures and crops, affecting farm production and profit.

See a WRC fact sheet here  and watch this YouTube

Waikato Regional Council has placed a “restricted place” notice under the Biosecurity Act 1993, on the Thames area infested.  This notice prevents unauthorised removal of soil material.

TCDC and other landowners must not remove alligator weed or any other material, which may have come in contact with alligator weed. A breach of a restricted place notice can have very severe consequences such as fines and/or imprisonment as outlined by the Biosecurity Act 1993.

No soil is to leave the complex while the restricted place notice remains in force.  All earth moving, tracked equipment must be washed down with a high pressure hose, to help prevent spread of alligator weed to new areas. This must be checked by Waikato Regional Council before the machinery is moved to a new site.

All mown grass must be removed from the area and taken directly to a designated site authorised by Waikato Regional Council.  Alligator weed infected material must not to be taken to a composting facility.


The owner/occupier is required to display signs provided by Waikato Regional Council at all entrances and exits informing of their status as a Restricted Place.

Alligator weed has been found in other parts of the Waikato, but this appears to be the first time it has spread to Thames-Coromandel. 

Please be vigilant and make sure you report any sightings of this highly destructive weed to Waikato Regional Council.  Do not attempt to eradicate yourself – seek expert assistance.


People sometimes ask why they pay Regional Council rates — keeping highly dangerous weeds like alligator weed under control is one reason of many.