Environment Waikato is working with landowners at a new subdivision in north Hamilton to deal with one of the largest infestations of alligator weed the city has seen.

Alligator weed is ranked as one of the top 100 invasive pests in the world and the primary risk of its spread in the Waikato is that is can clog waterways and threaten agricultural pasture growth.

EW ranks it as the region’s number one pest plant threat. It has surfaced at a number of sites across the region since the 1990s and the council acts promptly to contain it where it appears.

The latest Hamilton infestation, just under a hectare in area, located near the northern end of River Rd, is being sprayed with herbicide by EW and a restriction has been placed on soil and vegetation leaving the site.

EW pest plants officer Darion Embling said it was important to control the alligator weed infestation so that it did not spread.

"Alligator weed is a fast-growing pest plant that if allowed to spread can seriously invade agricultural pasture and clog waterways.

"It is reasonably rare in the Waikato at present and we want to keep it that way. Otherwise it could become a disaster to our dairying region and totally spoil our wetlands, streams and rivers."

Mr Embling said alligator weed was hard to eradicate and it could take years to get rid of the Hamilton infestation entirely.

This latest alligator weed infestation was identified by EW just over a fortnight ago and Mr Embling said the landowners affected were working closely with the council to ensure the pest plant wasn’t spread from the site.

"We’ve been getting great co-operation from the land owners and we’re confident that we have a plan in place to stay on top of this infestation."